Well....
I know a Border Collie from walking in the park. Rocky has been a humper since day one. His owner did nothing to try to stop him...I hadn't realized this would be the case until I had to pull him off Danny (who was much smaller than Rocky) when Dan's yelp and subsequent snarling did nothing to stop what was going on...unfortunately, that yelp seemed to be why he started favoring his right hind leg (a big problem as he aged).
Anyway. Rocky eventually got neutered and never stopped humping. He's approx. 11 now and at some point the humping proved to be domination and Rocky turned aggressive toward all other dogs.
I keep my dogs away from known humpers and resent it when owners don't at least state a warning when we meet. Neither of mine now can afford to have a dog mounting shaky rear ends, but I protected previous dogs, too.
I never had a serious problem with humping. My female yellow humped her chocolate brother's head while he slept...he didn't care. Dan humped his mother's shoulder a couple of times (scared himself by getting stuck outside and needing my intervention to get him back to normal). Most of the pups humped favorite stuffed toys for a while. With the exception of that yellow female, no one humped anything after neutering. Everyone mentioned got neutered at six months.
So...I have no training advice but recommend, based on Rocky, that you definitely try to keep him from doing this...for the sake of any other dogs he will be meeting. You don't want him starting fights...perhaps inadvertently...or hurting someone else's dog.