Is there a reason you cannot use a shim under the bushing like Bellm uses on the T/Cs? I would bet contacting him about it might lead to another option. He has some extremely thin stainless firing pin bushing shims for only $14.95.

http://www.bellmtcs.com/store/item.php?pid=1008&cid=243


2- .005" thick
1- .004"
1- .003"
1- .002"
1- .001"