Just keep playing the foreplay mode, even after the little lovemaking heart has popped up. If you just keep going, eventually he gets tired of waiting and will take over. It seems you always bottom in that case, though, fair warning!
Ah. Okay. The way they worded it in game made it seem like if you got his personality to be dominant enough he'd start calling you out on dates so just wanted to see if I was missing something.
Oh. But as far as the foreplay part goes, the only way you end up on bottom is if he's a top, meaning if you've been bottoming to him to the point his preferred role is to top then his subsequent "can't wait anymore" in foreplay mode leads him to fulfill said preferred sexual role. That's been my experience so far at least. ....And I've been testing it VERY thoroughly! ^///^