I went to a bond auto parts sotre which carries "Parts Master" house brand. There they had a 1/2 inch drive individual socket with a removable torx insert. The insert is basically what you're looking for. However, I think you may need more than that.
Mine was way too tight to use vise grips, and trying the bit insert alone with a 12 mm box wrench, I pretzeled a pretty decent Craftsman wrench. So I welded a cheap 22mm. box wrench to the outside of the socket. Even then, I had to wedge the socket into the torx head to avoid slippage, and use a 2 1/2 foot cheater on the wrench to pop it free. After it was loose, I popped the insert out of the socket and proceeded just used it in a 12 mm box wrench the rest of the way.
If you do it the way I did, and the box wrench has an offset, offset the box wrench inward, toward the tip of the torx bit. I used a flat steel wrench from a Yamaha motorcycle tool kit and bent it, but the principle is the same if you use a regular wrench.