Help! How to remove rounded trans plug??

[Stpndsmnn at aol.com]

I was going to change the fluid in the trans tonite..  Got it all drained out
and then went to loosen the top plug....   Well, it was tighter than a bull's
a$$ at fly time and the inside of it rounded out.  Now the Snap-on plug
remover starts to grad and the turns inside the plug..

Anyone ever had this happen?  What is the best/easiest way to fix this..

Thanks
Matt Kramer