Originally Posted by Shimagnolo

Do your pedals have steel spindles? Most likely they do.
So buy a pack of 1/2" x 1/8" magnets, then put one on the backside of the pedal spindle, then stack as many as you need to get close enough to the cadence sensor to trigger it. No need for any kind of adhesive. They will *not* come off accidentally!
I do this on all my bikes.

Here is a pack of 10 for $8.35: http://www.amazon.com/gp/product/B00...ls_o02_s00_i00