well if its striped already and your not gonna reuse the part.... just use a dremel or grinder or what not and grind the head off..... or drill the bolt out depends how much room ya got to work with....
i know on my old header i couldnt get the last shield bolt out from it being striped so i just yanked that sucker backwards enough so i could get to the head bolts to remove the whole thing as one piece.
it worked