I've modified a clamp assembly and it works great! This trick only works for certain profiles (WA,WB,WC,WG, WH, WY clamp up OK) but for those profiles it is good. Now I have additional keys for my WA Best cores.
The modified clamp is on the right. The W series keys are 40 thou thicker, so I had to remove about that much so it would fit correctly. The critical holding point is at the bottom of the key, and another important point is the tip notch, since that's the reference point for the location of the pins. The bottom of the key section is 80 thou for both WA and A, so I didn't have to do anything there. I had to remove material where the fatter part of the key bulges out - I made it flat so it would work with other W profiles.
This shows keys mounted in the modified/unmodified clamp assemblies.
The clamp assembly in the Pak-a-Punch.