Cat is at it Again!

A month or so back I asked for help as my cat had taken to humping my mothers leg at night. She was squirting him with a water bottle when he attempted to play Cassonova. It worked for a while but now he is worse then ever. He is not only attempting to hump her leg, he is humping my fathers leg and random bumps in the blankets. It wouldn't be so bad if he was at least quiet about it, but he meows and growls and generally acts like he is having a great time. This may be a dumb question, but can he possibly be getting any pleasure out of this? What else can I try to stop him. If he is locked out of the bedrooms at night, he just goes after the blankets on the couch. The problem is so bad that we have taken to referring to him as the "Horn Cat".
For those just joining the saga of debauchary, Greystone is 4 year old neutered persian male. He was neutered 2 years ago when we adopted him. There is some suspicion that he may have been a stud cat, as he was declawed when the shelter took him in, but he was not neutered. Any help would be greatly appreciated.

I've never heard of a cat humping anything and my first reaction was to laugh uncontrollably at the thought of it but I guess it must get annoying quick!

I know some animals do masterbate just because it feels good and if its not a dominace thing then I'd assume thats what it is. I kinda doubt it has much to do with him being studded out before. I know a couple of people that adopt old breeding cats and never heard of that,my male has been bred before to.

Can they just close the door at night? I have to admitt if I woke up to anything doing that to my leg they'd probally go flying through the air and learn its not a fun experience

Actually, since he has not made a move on my leg, I find it sort of funny too . If he is locked out of the bedroom at night, he humps blankets on the couch and screams like a female in heat. The bad part about that is the couch is seperated from the bedrooms by a hallway that acts as a tunnel of sound. When he gets tired of molesting the couch, he comes down that hallway and scratches on the closed doors. He is declawed, but that "whoosh whoosh whoosh" sound gets very irritating.