Hummm, maybe you can Play on both kinks at the same time. It seems like a good combination.

For the impregnation kink I think you're right about the power-play side. My gf loved to be handled like if she did not have a choice from time to time. She also enjoyed some breath-play. Of course she knew I would not choke her, but the feeling of air restriction and of being "powerless" would still excite her a lot.

As such, a good idea might be to pretend having forgotten your pills, and that you will not fuck him unless forced to. Of course with him knowing in advance that you might do that kind of pretend at some point and a code to let him know if this is for real and not some kind of play. Then it's up to him to choose when and where to hit you (probably without a condom for his fantasy to work, so be sure to have actually taken you pills ...), within the rules agreed upon, and up to you to pretend that you're not willing, that it's not safe and that you might get pregnant !
Maybe sharing your position with him on google maps so that he can track you might help. Also "inadvertently" sharing your planning in advance with him and planning a lot of places to be/activities/routes that would give him opportunities seems like a good ides.

Also, I'm curious, how do you meet somebody with such kinks in real life. This isn't something you're usually open about. At least I know I'm not about to share such interests with anyone unless I know for a fact they will accept that.