He's neutered...I have never seen this behavior in a neutered cat in all
my years of owning cats..has anyone here?

How can I modify his behavior so that this stops, without alienating
him? I don't want him to think I don't want him around...

I haven't had one who does the humping although I have read about others who do
here on this newsgroup. I think most of them just give the little guy a
stuffed animal or blankie of his own to hump when the urge strikes. Maybe you
could just distract him when he starts by dangling a toy in front of him? (I
was going to say maybe you could just play with him when he starts but realized
that might be misinterpreted as an X-rated suggestion.)

Candace
(take the litter out before replying by e-mail)

See my cats:
http://photos.yahoo.com/maccandace

"One does not meet oneself until one catches the reflection from an eye other
than human." (Loren Eisely)