Try my burr method- it works about 90% of the time unless the threads are rusted or loc-tited: grind the face of your torx bit so you get a nice burr (only 1/32" or so). Tap the bit (as in with a hammer), burr and all, into the screw head. The sharp edges will bite and the excess burr material will fill the gap. Works with torx and phillips!

I flatten the ends of all my allen and hex bits flat occasionally as they will wear to round with normal use. Just dont get it too hot....