If Charlie is going to be difficult to put in for a nap, I must admit I do put a DVD on in my room and Ben lies in my bed for 15 minutes until his baby brother is asleep. I do make him a part of the nap routine though. We read two books together in Charlie's room and then I send Ben on his way. He has his Thomas the Tank Engine table in his room so that can usually keep him occupied until Charlie is asleep.
I make sure I tell Ben that if he needs me, I'll be in Charlie's room and that he can come in, but he must whisper. He likes to make "tracks" all over the carpet in the house so that keeps him busy, but quiet. Sometimes I have a sticker book for him to work on. He loves dinosaurs too so stickers of dinosaurs work well. I get the kind that are easy to peel off just in case he would happen to put them somewhere they don't belong!
It's funny, I never really thought about this before I had Charlie, but boy is nap time quite the balancing act!
I can't wait to hear other suggestions.