When I recovered my seat on the LS I used a new drill bit that was just a little smaller than the head of the rivet. With my cordless drill it was a snap to cut through the head and flick them off - save the metal strips the rives pass through, and clean them up good, removing any rust etc. You can paint them if you like. Reuse with new pop rivets and rivet gun - <$50...
You'll want to do the seat recovering by starting at one end and going slowly, stretching carefully as you go, and do it on a hot, sunny day - or else have a friend help you with a hair dryer.