I've used the hair dryer technique quite a few times, but I usually take a wooden dowel close to the same size as the insert and gently tap them a bit to get them started once they're warm. The only time I had one crack was when I didn't heat it first (I was in a hurry)....the sides of the insert stayed in the hole - had to drill it out with a Forstner bit. So much for being in a hurry.