Is it acceptable asking to join a researcher in co-organizing their conference session? I have a friend at another university that I met at a conference a couple years ago. Since then, we usually make an effort to attend each other's sessions, grab coffee, etc. Last year he organized a session at our flagship conference, and I think he's organized a similar session several times before. I think it would be fun to co-organize a session together, but I would assume he's doing his usual session. Would it be rude for me to ask if he would like help organizing the session (i.e., adding me as a co-organizer)? Or is this the academic equivalent of asking, "Can I invite myself over to your house to play video games since I don't have a N64?"

For context, we are both at universities in the USA. He is an Egyptian-born Canadian citizen, and I am an American. He is a few years senior to me; he is in a semi-permanent research position, and I am a 4th PhD student. For the record, I don't think he would view this as rude because he is a genuinely friendly guy, and I think he could easily tell me "no." But I am more curious about the general etiquette of these things.
I would not directly broach the subject. If you want to judge interest, the kinds of questions I'd ask are:


  What do you have to do to organize a session?


If your friend mentions needing a co-chair, you could ask your friend if he has someone in mind. 

But do not ask directly to be a co-chair for someone else's session. What you might instead want to ask is: "would you like to be co-chairs for a future session sometime?"