If you can't find something, look for a backpack with cinch straps on the top, you can put a strap on those to attach to the handle. I know for example many northface bags have them.
Like the dark grey strap in this one
It's not the best solution, but with the right sized strap or bungee cord works great
Also some suggestions in this thread
http://www.flyertalk.com/forum/trave...ge-handle.html