TL;DR - No, you are not allowed. It's prohibited in the Social Contract.
This is in the Social Contract you agreed to play (and which the other player would be required to agree to in your hypothetical situation): "Your account in the game is yours and yours alone. You may not share it with someone else nor give it to anyone, not even temporarily."
Ah yes. I went to look for hard rules but didn't see that for some reason. Sorry for wasting your time
