The issue here is common with Alembics and many through-body instruments. The problem comes from too much of a good thing. When you have through-body construction, one of the great things is that you can get rid of a lot of the wood at the neck joint since you don't require a lot of material where the neck and body pieces join (e.g. the neck pocket on a bolt-on or the dovetail area of a set-neck). Now that you can slim that area down, you can create a lot of access to the high frets and the cutaways can reach a lot deeper in than on a more conventional instrument.
But all this shifting can really mess up the balance. If you look at a P-bass, the strap button position is over the 13th fret or so; for a large-body Series bass, it's over the 18th fret and for a small body (like Stanley Clarke's instruments) is probably over the 20th fret. That's a big shift.
It's not an accident that the P-Bass horn ends up over there - it's pretty much extended out to the zone where the instrument will balance. The balance of a Series bass won't be like a P-bass, but it's inherently less balanced, which is the cause of the neck dive that people complain about.
There's a temptation with any through-body design to shift things around like this, although you often see a long upper horn to compensate (check out a Tobias, Rickenbacker, or old Veillette-Citron). I think this comes mostly from the fact that a through-body can give much better access to the high frets, but will look really odd with a super deep cutaway on one side and a regular one on top of the neck.
There are actually a number of very interesting workarounds that have come up. One of the best is the pivot plate/boomerang system on the Steinberger L and XL basses. These are the original boat-oar models that are truly the boiled-down essence of a through-body instrument (these original instruments are a single-piece composite construction). There's a gigantic bolt near the center of mass of the instrument that attaches a boomerang shaped plate that can rotate somewhat freely. The strap ends both attach to the ends of the boomerang. Since the pivot is at the center of gravity, the instrument's natural tendency is to pretty much stay where you leave it - it's very neutral. Since the strap ends are both ending up in front of you, the weight distributes more evenly as well. The balance point is quite a ways back in the body because of the mass of the composite material as well as the lack of a headstock and tuners at the end of the neck.
Ned Steinberger must be really interested in solving this problem because he has used straphook extensions on other instruments as well to improve feel. The NS/Bolin bass has a singlecut body design that wouldn't normally balance very well, but has a rotating straphook that extends out to the P-bass position. (They're no longer in production, but you can see pix on eBay under bolin ns.) I have one of these basses, and it's a pretty good idea that doesn't really work very well (they needed to make a locking straphook instead of one that just flips out like this).
Ned must have realized this because the Steinberger Synapse, a modern wood instrument that's vaguely reminiscent of his original stuff uses a fixed metal strap hook extender. You can see a little of it here -
http://www.steinberger.com/XS15FPACST.html If you're willing to perform surgery on your Alembic, you can probably try out Ned's NSDesign Boomerang Strap System (
http://www.nedsteinberger.com/instruments/systems.php#boom) which is a sort of recreation of the XL design that was created for people who wanted to play the NS Cello like an electric bass. It's a pretty sophisticated design with a friction clutch where the big screw was before. You can adjust the arms of the boomerang to be comfortable for your position and set the tension of the clutch so the instrument stays where you want it to. NS Design makes a modified version for non-NS Design instruments. You need to mount the big clutch at the balance point of the instrument, and I have no idea whether that is even on the body for some of the more radical Alembics. I haven't tried this out myself, but know the guy that sells the modified version for non-NSDesign instruments (it's from NSDesign, but they don't provide support for mounting on other instruments).
Finally, on a slightly unrelated note, there's work on the other end of the strap too. The problem of all the weight ending up on one shoulder is somewhat inherent in the traditional design. There was an interesting strap that just appeared in the last year for golf bags, called the Ogio Schling, which replaced the traditional over-the-shoulder or backpack-style straps of a golf bag. I guess it was a little too interesting, as it appears to have disappeared from the market already. It was a pretty interesting idea - there was a big rigid arm that was like a yoke that fit over both your shoulders. From that a single strap extended down to the bag. When you wanted to pick the bag up, you lifted the entire yoke over your shoulders and it distributed the weight across both of them. It was all an interesting trick of balance. You can see some pictures of what the yoke looked like here -
http://www.golfblogger.com/index.php/golf/comments/ogio_flight_ss_schling_stand_bags/. Something like this would definitely work for a bass too, if you could suffer through the R&D of making it happen.
In all these cases, the real challenge is that you want the ends of the strap to join as close to the cente of mass of the instrument as possible.
David Fung