is it possible to extend car permit w/o going to the border

[doncoulter]

With an FMT, you have no option. You must go to the border. Turn in your permit on the Mexican side, cross the bridge into the States, then return to Mexico for a new FMT and a new permit.

Fact is, you've been violating the rules by leaving your car here while you've flown out and back again. Don't mention your comings and goings to any officials at the aduana, and hope they don't notice that your current FMT doesn't mention your car.

Don