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Consider welding a nut or bolt to the head of the Torx (assuming you can reach it and that it is a steel bolt). Oftentimes the heat of doing this loosens the bolt. The welded on object gives you something beefier to wrench on.
First, try smacking the head hard with a hammer and a hollow punch such as a pipe nipple so as not to damage the torx socket. Hitting it hard compresses the metal under the head and will help to loosen it. Good Luck
....another trick, if you've got fairly *clear* access is to take your Dremel with a cut-off wheel & slice across the head, through the middle - basically making a slotted screw... use a flat blade screwdriver to remove it
I glued the bit into the Screw overnight with Gorilla glue, thats how I got the front bumper bolts loose on my Aerostar. Couldn't heat them because of the plastic bumper cover. Heated them with a heat gun and dropped the bolt and bit into ice water to break the glue bond. We used a glue at work that had a catalyst to break the bond, but can't think of what it was we used.