if you havn't boogered the hex part up you can carefully cut it off and put a 6 POINT socket on it. Warming the engine up first may help to losen them some too. Exhaust will come out of the tube if you cut it, just so you know so I wouldn't warm it after you cut. Warm it up cut,remove,plug then repeat for the other side.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!