will this work?

There are of course many things that can be done, but I think that the easiest would be to eliminate the connecting bar and notch the frame to squeeze the bag under it and centered with the lower bar (even if you need to move the lower bar out a little bit. But if you really want to make a cantilever bag mount, what you have drawn will work fine (assuming that all of the little issues are taken care of).

Keep us posted, I'd like to see what you come up with.