I recently had to do one on cozmeisters head, as same thing some numpty fucked up the splines.
Just stuff some paper towel around the bolt hole etc, you can always wash out any swarf afterwards.
On cozmeisters car it was a rear one right next to oil return, so I simply packed the return with paper towel, then drilled a small 5 - 6mm pilot hole about 3/4" deep in centre of bolt head, then worked up in 0.5mm steps going to the same 3/4" depth each time, when it had worn through the outer "ring" that remained of the bolt head it simply let go, pulled drill out with ring still on bit, then lifted head off.
Head bolt material if stretch bolts is VERY soft, due to it's inherrant elastic nature, just be careful when using the larger size bits if the are cobalt(as mine are) as they are seriously sharp and bet to drill at a angle as best you can to start with when you feel the splines grabbing the bits, then straighten up drill, took us about 30 mins but all was well.
If you do decide to use any easy outs etc pray they don't snap,(which is likely) as you really will have problems trying to drill this material without it slipping off into the softer surrounding material.
As I see it you already have a "guide" there in the bolt head so use it.
tabetha