Just skipped back through to look at the scenes in question. There's no way he's the singing android or 'Saunders' (the Android who keeps being called back to be told something else).
There's one Nestor with no dialogue who he could be but I'd bet against it if I had to commit.

http://www.imdb.com/board/20332944/
This guy is the Nestor tortured by Sador. Hes listed as Nestor 2 cos he's the only Nestor other than Earl Boen that has dialogue.

I thought he was the android, that the doctors daugther was putting back together when jonboy comes in, the one singing like a choir

Possibly, but the lead Nestor was older than the other clones, both in voice and appearance. The Nestor tortured by Sador was younger and with a slightly higher pitched voice. This is the one we are surmising was played by Brent Spiner in an uncredited role.
"I'm not really me. Thats me there- that pile of albino mouse droppings!"

No I think the lead Nestor guy was the same dude who played the psychiatrist in The Terminator. The voice gave it away for me.

There was another thread on here saying the same thing- it was the Nestor who was tortured by Sador. If it was Brent Spiner then he either used a different name or was uncredited.
"I'm not really me. Thats me there- that pile of albino mouse droppings!"

Im pretty sure that's Mr.Spiner right there too.

No that was a guy called Whitney Ryback (or something like that). Hes in tonnes of stuff around the late 70s early 80s. He play's a bomber/spy in the Buck Rogers episode Plot to Kill A City, a sailor at the jitterbug contest in 1941, and one of the tv crew in Rocky II when Rocky is trying to advertise Beast aftershave!

Actually, if I had to guess, I bet he was Hephaestus's assistantthe one who keeps turning to leave as the Dr. keeps talking to him.

That's what I'm thinking. Thanks
I don't know a lot about anything but I know a little about practically everything
Vincent Price

I agree. I think he was in this as one of the Nestor guys.