Turns out I am not the only one that struggles to keep the brackets securing various devices to my handlebars in working order. I have broken tabs off of all sorts handlebar brakets meant to hold lights and cyclo-computers. A common hack is to use a rubber band to help hold the computer in place.
Dave from crossgeared.com encountered a similar issue when his bike (he does not specify whether or not he was on it at the time) unexpectedly met a stream bank (his words). He experimented with zip ties but his final solution came with an inner tube. He states:
As many of you know, inner tubes are very useful for a number of purposes other than holding air in your tires. My new mount uses a standard 26 x 2″ mountain tube (I’m guessing it is a 2″ tube, I found it on the trail), and that is it. I just cut a length of tube, cut a window for the computer display, and then another hole to fit around the mount base. Normally I’d give a procedure or some simple instructions, but since all you have to do is cut two holes in an inner tube I’ll just post some photos.
Here is one of his photos to get you started, jump over to crossgeared.com for the full picture show.