Since you have a U-lock mount, what I do -- coil the cable, run the U-lock through it, hang it on the bar -- won't work for you. What you COULD do, though, is coil the cable, and hook it with one of those decent-sized caribiniers from Wally, and hang it THAT way on the bar.

If you coil the cable down to about the size of a roll of ductape, it will carry just about anywhere.