A W-I-D-E strap may help. The ones in our online store are 4 inches wide and have a pigsuede underside so there is a little grip to the strap.
You can improve it slightly with lighter weight tuners, since they are way out on the end of the peghead. Skip the idea of ballast - you have to add so much to make an impact that you really can't enjoy playing the bass anymore.
The balance is all about the length of the upper horn. The closer it is to the twelfth fret, the better the balance. The Persuader uses a Spoiler body shape, which was originally designed as a 4-string medium scale bass. If we add another tuning key, a wider neck and a longer scale length, the shape is not performing at its best.
So you can try a different strap and lighter tuning keys, but if the shape just isn't suited to you, then you should probably consider a different shape. Note that some people play long scale Persuader 5-strings and are completely comfortable with the balance.
Exploiter body shapes balance extremely well. Other well-balanced shapes are: Rogue, Europa, Essence, and Balance K (hey - Balance is its first name). You would probably want to stay away from the short scale Stanley Clarke models too based on your experience with the Persuader.
