Update: Irritatingly, Lili is generally good as gold for DH on the somewhat rare occasions that he changes her (consequently, he's started dealing with post-bath nappy and PJs). I thought maybe it was just the novelty factor, but after observing the other night I decided to try his tactic of telling her not to move ("Lili bouge pas!"). It, um, seems to work.
Lili's quite a bit older than Iris so that probably won't work for you, but I thought it was quite a breakthrough! She's not talking yet (apart from "uh-oh" and "pa-pa" - I am obviously too important to have a name ), but she definitely understands things like "Lili get in her chair" when it's time to eat, and "shoes" or "go outside/in the car"). It's all very cute!