Does your friend have a sense of humor? I yes, I like your idea of making a pieced backing using the signatures. For those blocks that are signed on the back side, make a flap where one side is stitched in place and the other is held down with velcro! Everyone needs a good laugh and, after all, it is the thought that counts!!
Anyways, bikers are supposed to be good riders, not necessarily quilters. :-)