I would nip it in the bud, make a distracting noise or distract him with a toy, can't be much fun for the bitch! My pup humps cushions (before eating them ) but I just take them off him.
Sleeping off a very busy day yesterday, there's a piccy thread down there somewhere, he's doing great, never stops, fantastic attitude, everyone who meets him becomes a fan! You've it all ahead of you