Pop off the plastic on the back of the rear hatch. That should allow access to the back of the plate bolts to remove the one with the messed up head by pulling it from the back or pushing the other through too.
im having this problem now and the bolts wont move with 5 different drill bit/extractor kitsthanks, I got the hatch panel off...but the bolts are very hard to get to because of a big metal piece that goes over it..hard to explain...can't get pliers down there...