Most of the time (if it's only one plug) I will go ahead and let it run up to operating temp and try to get it to clear, and it usually will. But I don't like washing down that one cylinder for 15-20 minutes until the plug starts firing!!
A couple of years ago, I made a set of those "car skates" that go under the tires just so I could move the car around the garage without having to fire it up (and foul a plug)!!!
I guess I'll just have to live with the problem for now, but thanks for your help Michael.
Steve