Here's a pic of the heel-toe shifter I rigged to my previous bike - a Suzuki VX800. It looks gerry-rigged, but I've ridden it like that for around 50,000 k.m. with no problems, and the action quickly became quite natural. Also, the toe of my left boot has thanked me for it many times - particularly when it rains! I'm going to have a shot at rigging up something similar to my BM. I'll post up my progress.
Cheers,