I attached a template (edit: it's a zipped EPS let me know if you need another file type), best I can do at least. I don't have anything that will print large enough to test and there are two other problems:
Our taillights have a compound curve to them (they bend along two axis). I don't know how to accommodate for that exactly. Using vinyl you should be able to heat and stretch if necessary...
Parallax - since the lenses are beneath the surface of the taillight (where the overlay would be) they have a different apparent position depending on the angle from which you are viewing. not a huge effect, and I tried to account for it by sizing the cutouts a bit smaller than the lenses.
Also, I added around .25" around the outside to allow for cutting after placing on the vehicle.
So, anyone feeling brave?