I've trying to find the thread where it was explained(with pictures), but I can't seem to find it.
Anyway, what I did with mine was I cut a small piece of cardboard the exact width of the strap(at the clasp end). Then, I cut it to about 3/4' long, placed it on the strap between the clasp edges and taped over it with black electricians tape. For some reason, the black color of my tape matched exactly with my black strap and it looked clean!
I put the watch on...and no more pain! I had wanted it to be a temporary fix, but since it looked clean...and you can;t see it at all when you wear the watch, I kept it as is. Just mack sure the cardboard is thick enough to be just a hair taller taller than the protruding edges on the clasp.
I had seen on another thread that another way to do it was to file down the sharp edges, but I was afraid to do it because I had never done it before...and it was one of my first rep watches!
I hope this helps. May the New Year great you with painless wrists!