I was hoping that someone who bought a small plot and later upgraded to a larger one would know. I've tried submitting an in-game ticket, for which I got a runaround scripted response saying I should ask other players on the forum, since they can't help with gameplay issues. Which sort of brings up the question of what they CAN help with, but anyways.
I think at this point its pretty concluded that there's no way to transfer land, so I'll probably just have to hope that changes in a patch.