I actually just tried this and it worked amazingly well. I cut the DC jack in half (horizontal to the motherboard) with a dremel. I then was able to see the pins that were soldered to the motherboard.

They were no longer part of the jack which I think was acting like a heat sink when I was trying to unsolder the pins before. I just unsoldered the pins one at a time and removed them. The only thing you really have to watch out for is that the dremel does jump on you while you are cutting.