I guess I must have cheated. I held the rubber pieces in place with vise grips (or ?) and just drilled through the fender and rubber together, enlarging the hole slightly on each one. OK, here's where I really did cheat, I used some aluminum mechanics wire that I had and cut short pieces of it and pushed it through each hole, bent the ends over with a pliers and finished them off with a couple taps with a hammer to flatten them nicely.