Any type of mylar has to be subbed using something like the electron bombardment treatment Chris mentions above. IDK if there is a solvent for PET as I have never looked for one. Subbing formulas require a dilute solvent to soften the material and make a more "friendly" layer stick to it.
Graphix, on the Dura-Lar page, mentions a "Prepared (Gel-coated)" material. This might be interesting. Anyone know anything about it?