TroyO,
Don't bother, I have tried to drill them out using diamond coated tube drills designed for drilling glass. All it did was rip the diamond coating off.
The only thing that I think would be successful is spark erosion.
BTW, UNC is very close to Whit threads, and in a lot of cases, either mixture will sometimes screw together enough to clamp up and get you going. Plus Mr Whitworth was the man who got everyone to standardise their threads, and without him, you people would still be hand making nuts and bolts for individual fitting, so don't knock it.
John