Not sure if it still works, I'm pretty sure they had patched this the last time I tried. If not, then I'll probably just get MineCraft and Trials Evolution.
The only downside is that you have to sign onto the modded account first, EVERY TIME, and it's really a pain in the ass. Probably just have to buy the games eventually, but for now, I'll put up with it.
Thanks @OP, even though I knew it years ago. Still reminded me of it though, so props to you. ^^