Two pieces of material around either side
-the B44 hardware posts
(You're basically slimming the saddle setup by narrowing the "pocket" but you use the same hardware for the posts.)
- use the saddle pack hold down at a Diagonal.

couple drilled holes to make it work and it'll look good too? Maybe someone's got an easier idea.

Or a Battery Velcro tie down? Kinda ghetto but it works.