It was black cardboard wrapped around his (run of the mill) keyboard stand. It was there to hide the mess that was underneath it. He played two Infinite Response VAX77 Keyboard Controllers playing samples from an off stage computer (Mac). I don't think he was trying to make it look like a Mellotron at all.
In a message dated 6/23/2010 7:18:02 P.M. Eastern Daylight Time, wonggster@gmail.com writes:
Eddie Jobson's mellotron shaped keyboard stand was a piss.