Here's an idea:
Jim Dunlop (I think I have the right brand in my head) uses a Strap-lok system where you could use either a normal strap with no locks on it OR a locking strap complete with their particular clip-on to the strap.
Here's the one I'm talking about.
So, you could install this strap button on the bottom of the bass, and adjust your strap how you like it.... and then, cut a hole in the same strap several inches higher than the end of your strap, and install the strap lock. All you'd have to do then is reach around and grab the strap lock and insert it into the strap button for the higher position, and then remove it and release, and whammo, you're back where you were.