I did my 240s park lights the other day haven't got around to the headlights.
I used the cardboard box and hairdryer trick with a towel draped over the top of box, it worked well . I was a bit skeptical about putting them in the oven in case they touched anything metal and getting big grill marks in them.
I found out pretty quickly that if it doesn't come off easy its not hot enough.
Didn't turn out to bad, they had small stone chips on them anyway so the stress factor wasn't very high