There's a harness sorta strap that comes with the Warr guitars that holds the instrument in place quite well, though I can't recall the name or.brand of it that might help with some of the"not-quite-so-light" models from the swellest bass makers on the planet, could help with neck diving as well.
I had never considered the harness for use with series basses until reading this thread just now....wonder where I put that thing?