Have done this twice when I had a fiesta z tec s and a fiesta ST. I just used a hair dryer and that did the job, just took a while though. other people have put them in the oven to heat the glue, just be careful if you are to do that though. Oh and when there put back together just be aware to make sure to seal them properly as other wise you will end up with condensation forming in the light.
PH2 lights are "permasealed". No way a hairdryer will split them. You need to be much more aggressive.
Was going off the principal it myt have been the same but obviously not the case. Oven method then or heat gun?. Is this something you have done yourself?