The internal SD cards are in a completely different physical format than micro SD cards we're all used to. The micro SDs are made for transportation/transerinf purposes. The internal SD cards are soldered onto the motherboard inside the phone. I'm sure it can be done, but there's a good possibilty that it could completely mess up your phone rendering it useless. So, I would say that it's not a good idea to do so. Especially yourself. I don't know of anyone trying to do that kind of modification.
Sent from my 3rd reincarnation of the ever-so-lovable Droid