Drill the center of the bolt head with a 5mm (or 13/64" which is close enough) drill bit just deep enough until the bolt head pops off and rotates with the bit. You can then take the cleat off and remove the bolt stub with pliers or a Vice Grip. This will save both the cleat and the retainer plate inside the shoe. I've done this a couple of times and it really works.

Next time grease the bolts before installation.