It's possible to get those off if you have the right tools and work carefully, as long as the Torx was loosened a little and you can see a little of the shank of the screw.

Get a Dremel tool and put a cutoff wheel on it. The larger, fiberglass reinforced wheels work best for this type of job because they don't break as easily.

Have a friend grip the end of the Torx screw with Vise Grips while you carefully cut through the shaft of the screw with the Dremel tool. When it's cutoff, push in on it and it will fall in, landing on the floor.

If the Torx screw isn't backed out at all, you're going to have to hold onto the nut with a wrench or Vise Grips. It may be possible for you to reach up under the dash and get a wrench on the nut. In order to get more room, depending on your dash, it may be easier for you to remove the glove box, rather than the entire dash, if the loose nut is on the passenger side.

After you get it out, use a NutSert or ThreadSert to provide a fixed, threaded hole in the spot. Naturally, put Anti-Seize on all bolt threads when you reinstall it, in order to prevent this from happening next time.