Try and get some penetrating fluid/Plusgas down the threads, keep giving it a bit more every half an hour or so for a few hours, then as Alex says drill a hole down the centre, start off with say 3mm, then keep opening up to about 8mm ( I think it is an M12 thread/stud) then hammer a Torx bit into the hole, more plusgas and gently tease it backwards and forwards and keep adding plusgas, it will come out eventually. You could also try heating the hub with a blowtorch, then cooling it with water, muliple times, keep going with the Plusgas as you do it :thumb:
When contemplating jobs like this on my cars I always plan ahead and give all fixings a few doses of plusgas over a few days prior to starting work on the car, obviously you can`t really do that with the caliper bolts due to the length, but it really does make life easier :grin: