Assuming they're similar construction to the ones on the 3 then no, you can't bake them open. The tail outer cover is actually melted around a lip on the housing itself. You could (and people have done this before) very carefully cut through the part melted around the lip and then try to glue it back on afterwards. I saw once where someone tried that but couldn't get it to look good afterwards. He bought another set of cheap tails, cut the housing off of the outer cover and was then able to pop those lenses onto his original housings.