You can either grind off a couple of threads with a dremel tool, bench grinder or use a file
be sure to go slow to not create to much of a burr on the end of the threads
if you have a 1/4 28 die to chase the threads it would help
if not screw a 1/4 28 nut on the bolt before you start grinding ( if there are enough threads on the bolt), then back the nut off after grinding the threads off

another option would be to use a couple of small flat washers between the screw head and the stock- this might be the easiest option if you have the washers
Jack