As far as I know (and I may be wrong), but opening up tailights is not as easy as with headlights. With headlights, they are sealed together but taillights are more so one whole piece. Therefore, baking them in the oven doesn't do much.
However, if you look around, I believe there's a thread about opening up taillights. I think the guy used a soldering iron to heat-cut the damn thing open.
Whatever you try to do, good luck!
Let us know how it goes.
Edit: Here's the thread .. turns out a dremel was used.
http://www.ft86club.com/forums/showthread.php?t=38101