Hi there Racing Snake..
Was just wondering how you got on with this? Have identical problem and am just considering using an "easy out" drill bit to drill it out (hopefully) after some soaking with Plusgas! Would love to learn from your experience as the frame and seatpin is well worth saving!
As long as the thread is ok this should be fine. Don't shear the easy out though or you will have problems. In my case the thread was ruined when I got it so I had no choice but to go bigger.