Giving players velocity / "attaching" players to objects?

I've been thinking of the possibility of creating a raft made of twig models to let the player cross large bodies of water. I can move the raft itself, sure - but could I move the player somehow, along with the raft?

I'm going to bed soon, so the question is purely theoretical. I'll most probably give it a shot when I wake up, but I wanted to ask just to see if I should even waste my time on the idea.