i used to tie a weight to a short length of broomstick, maybe a foot or so. roll it up, roll it down, roll it up, roll it down. you can also get grip excersizers with springs or rubberbands. you could also make your own, if you're handy. something like a ring, wood might work, and some hooks in it, rubberbands or springs to the hooks, then metal rings (old keychains would do) to the end of the springs/rubberbands to hook your fingers in. dang. now i have to go try and build one!!