Is it possible to enlist a TSX to an MSX in a different domain?
The answer is yes, if


The two domains have sufficient trust relationships configured, or
You can figure out how to set it up using pass-through authentication (I believe this requires running SQL Agent under matching accounts).


Here is the Master Server setup screen:



In other words, there is no bypassing Windows authentication.

IMO, if there are no trusts between the domains, and there shouldn't be for business or security reasons, I think it would be a better idea to set up a new master server in the other domain, instead of circumventing security just for this.