The Mellotron Group

A question for those with talented ears: I'm going to put some Tron down on a tune recorded by a mate, and I was hoping to get a sound similar to that which Bob Ezrin pulled off on Caroline Says II on Lou Reed's Berlin. Trouble is, I've tried a few things and nothing sounds quite like it.

Here is Ezrin doing his thing: http://www.youtube.com/watch?v=7TOlgGUcWaE#t=90

Obviously it's double tracked, but there is something very odd about the filtering. Anyone got any ideas?

Mike