The only time i have this problem is when the raid leader is a honor bot, since they autoqueue and are usually the first person in the raid. Which is about 50 percent of the time if i do avs past 1am. I find that you have to send a whisper to the person, asking in the /bg channel doesn't seem to work, and it is important to ask if they will move you before asking if they will promote you to leader. It seems that some people get off on being a raid leader and they get upset if you ask them to hand it over, even though it really means nothing... It also helps to tell them the group number your main is in, I usually whisper something like "would you mind moving all of the characters with the name <name> into the same group or promoting me to leader? I'm in group 5." Works every time, unless of course it's an honor bot then you're sol.