I had the same problem with DD when DS came along. She is very attached to her bedtime routine, and DH is away for two weeks of every month so I couldn't just hand over to him. I ended up buying a small portable DVD player that she watches on her bed when I am putting DS to sleep. She is only allowed to have it then, whether it's five minutes or half hour, so it's a treat for her. As soon as he's asleep, I go in and do her bedtime.
It might not be everyone's idea of a good solution but it works awesomely for us - everyone is relaxed and happy. Definitely some of the best money I ever spent.

Good luck!