I can't vouch that this works 100%, as I've never tried it myself. I've heard that if you remove the cables from the 12V battery, then put them back on, that it'll unlock the car. Again, I haven't had to try this myself yet.
I'd highly recommend getting a second key fob at some point after you find a way into the trunk.
I'd highly recommend getting a second key fob at some point after you find a way into the trunk.