Well another loophole has been exposed on the SD thread.
http://slickdeals.net/forums/showpost.php?p=72553810&postcount=14570
It works with either a TDP or a basic line to receive the upgrade and results in you getting to repeatedly upgrade the same line over and over again using the 4ever method. I don't have any upgrades to test it out, but in theory you shouldn't have to use a UDP line's upgrade - any line should be able to be the upgrade donor line in theory. But since the SD thread is about UDP upgrades, so far at least that is all that have been tried.
I have already warned others about my experience here and on SDs so proceed at your own risk if at all. After what I went through, I wouldn't do this. I don't have any upgrades to do it with anyhow but as I now know, Verizon can blacklist all of the IMEIs of the devices.
http://slickdeals.net/forums/showpost.php?p=72555932&postcount=14572
I am just bummed that this loophole exists b/c people are going to abuse it and Verizon is going to fix it and when they do, they may fix all of the loopholes that allow us to upgrade our UDP lines.
🙁