Of course it‘s possible. A working portal can be checked/marked by the game and it can compare the marked coordinates with the player ones. If there’s no other marked portal and/or it is the nearest, the compass direction is pointing to that portal. The only interesting thing would be, when the player comes to a range closer to an other portal. So the game has to check all the time what the nearest is.

A other idea is simply to say, that the first generated portal is and stays the one where the compass is directing at. But here’s the problem: What is when it gets destroyed.

It is technically easy to do. But it needs some conception time ^{^}