Sometimes we want to use products in a different way than they were intended to be used. Reader Steve had a handlebar bag, but he did not want to use it on his handlebars. He wanted to do a 180 with it so to speak. Text and pictures below credited to Steve. More photos can be found via uploads Steve made to Dropbox. Take it away Steve . . .
I used a Gibraltar SC-PUGC clamp, although most of the major drum companies have an equivalent (like the Pearl AX-25). It's holding a piece of handlebar tube courtesy of my local shop (http://www.freezethaw.com/), and my mounting bracket goes on there. I put my extra lock through the tube for security. Voila! Handlebar bag on the back of my bike!
And with the bag attached . . .