I picked up a nail in one of my F1 run-flats, had it plugged externally, and have driven many thousands of trouble free miles. I have had many external plugs in many different kinds of tires over the years and I have had only one plug that would not seal properly and ultimately required an internal patch. The fact is, with run-flats a failed plug is not as critical as it is with a non-runflat. A failed plug is really no different than picking up another nail. If you have run-flats, you can keep driving whether it is a failed plug or a new nail. While a plug might have an effect on the speed rating, I don't think integrity of the tire is an issue in this case. The tire is not going to disintegrate, wreck your car, and kill you because of a failed plug.