[Small Fry]

Personally I never feel any obligation to stay. I will give advance notice, maybe 30 minutes, maybe one round, of when I intend to leave.

So who's home is it? Does he act the part of host? How is the decision to change the stakes made? Majority? Everyone has to agree?

If you have a "host" just inform this guy at the start of the game that you will not agree to up the stakes. Or If the stakes are raised then you will most likely cash out.

If everyone has to agree and you're comfortable around all the players inform the entire table at the beginning of the night.

Sounds like you enjoy the "friendly" lower stakes but have some concern if the stakes get raised and it becomes "real" money. If this isn't a concern then I don't understand your reluctance as you say your comfortable at increased stakes. If you concern is other players, then tell them to speak up. I assume you're all adults.

Lastly you could try ignoring him. When he asks the first time and you say no there is no need to respond again. Until he asks you directly. You can then inform him that you already answered that question.