Good news, everyone. I managed to "fix" the jaw enough to where I'm comfortable with it. After using a blowdryer to soften up the joints, and deepening the peghole with a thin pair of scissors, I eventually managed to get the peg snugly into the hole. The peg actually popped out of the upper jaw while I did this, but it was a blessing in disguise. After letting it sit in the freezer for 30 mins, and then returning to room temperature for another 30, I added a layer of duct tape over the back of the lower jaw where the peg would be exposed, to give it a little more grip and stability. After heating up the upper jaw and reattaching both pieces, i let it sit in the freezer for another 30 mins and then defrost again. i reattached the head to the body, and the jaw, while still a bit loose, stays in just fine. I'm almost positive it's due in no small part to the sturdy duct tape.
So that's it. My G2K is "fixed" and I can finally start waking up the joints and taking pictures. Thank you everyone for all of your advice.
