One of my friends had asked me about how to keep chatting or working on facebook and show IDLE status on facebook and I didn't find any ways to force facebook's chat to go IDLE.

I know that in order to have your status Idle you must not use facebook for at least 10 min, if I am not wrong. But, I think there should be some way to change the status for chat, right?

Does anybody know how to do that?

Note
Don't propose to go offline for a chat. He knows it already, but he doesn't want to be offline on a chat.