It's in the Quadrilogy somewhere! Veronica Cartwright was talking about it.
There are a few of the model makers from ALIEN in the forums at Alien Experience, and one of them related a story where Bolaji pinned Yaphet Koto and sat on him, all in the Alien suit, to get him to stop being so against the idea of being taken out by the Alien.
I don't think anyone got a picture