If worse comes to worse, you can either smash out one of the taillights, although that will probably bend sheetmetal you don't want to bend, or take the back seat out and pound out the skibag hole so you can gain access.
I'd vote for the skibag hole, myself, and I happen to have a skibag you can buy from me to fill it up again!

Of course, you'd then need to have an armrest rear seat, but I also have a gray cloth one of those available!
You could also just put your seat back in, but where's the fun in that?
Short version: remove rear seat, get hammer, pound out skibag hole, try to open trunk from there.
