All her life Rey hastaken suppressants. They are in her rations, and she dare not go without them. She can't afford to give away that she's an unbonded Omega. But once she leaves the planet, strange things begin happening, and Poe walks in on her, needy and desperate. He does what any decent Alpha would do... Tries to take good care of her, and ease her pain. With the sex.

Alternatively: All stormtroopers are given suppressants. There is no question of dissenting. But now that Omega!Finn has a name and a purpose, he wants to be free in every way. Alpha!Poe is there to help. With the sex.

Bonus points for making them an Alpha/Beta/Omega bonded triad!