All of the cleat bolts I've ever seen are M5 so this method is base on that size. Adjust as required if your bolts are larger or smaller.

1. Use a 7/32" drill bit which is very slightly larger than the 5mm bolt's shank but smaller than the head.

2. Center the bit in the remains of the allen key recess and carefully and slowly drill just until the head of the bolt pops off. You do not want to drill out the entire bolt, just decapitate it.

3. Remove the cleat.

4. Turn out the bolt stub remaining in the shoe using pliers or a Vise-Grip.

This technique is a proven method for removing damaged cleat bolts without damaging the cleat or the shoe. Guess how I know.