I am a groomer and I always take a cotton ball and pull it in two (or appropriate size) and stuff it in the ears. Not too far where you can not get it out but enough to make it stay for the bath. DON'T FORGET TO REMOVE IT AFTER!!
Definately helps to prevent ear infections!
Oh...the sooner you get the puppy used to the bath the better...just make sure he is completely dry when he is done so he doesn't get a chill.