I just recently took a 15mm open-end combination wrench out of a set (VW does not make use of 15mm fasteners - so it will not be missed
), and put it onto my grinding wheel to narrow the head from about 7mm thick down to maybe half that. Tested on a set of old Look pedals and some SPDs - works like a charm. Total cost: $0.02 (in electricity, I'm guessing).