Here’s how I did it.
I went to the coordinates, and found a place to build another Nether Portal close by that wasn’t protected. I went through and then had someone destroy the portal behind me. Once in the nether, I found the one that linked to where you’re trapped and went through. Have someone bring plenty of obsidian and a lighter. Two portals may be required (I chopped them down, so yea) On the other side, I threw an ender pearl to get over the gate.
So, if I’m not on, but you can get in touch with someone, somehow, via Skype, TeamSpeak (reminder, we have a teamspeak server set up for us) or the forums, have them do the same thing and bring extra ender pearls. I know you can’t type while stuck in the portal, but you should at very least be able to hit Q and drop something so you can make room to pick up the pearl. Once you’re freed, just teleport out to a res or spawn.
I work 2nd shift every day, so I don’t get on until really late at night, so I might not be the best option for you if you’re impatient, but if I am on at the same time as you, I’ll make it my priority.