just ask the chef?
I know exactly what you mean though. I was wondering the same, so I asked the chef (my old schoolmates dad) and although I was very drunk at the time, asking him how they were so nice, I recall him telling me he used liquid egg, or egg / yolk powder as an ingredient, in a very hot 'used' wok. He said I'd be able to find it in china-town in one of the chinese supermarkets.
I'll ask my mate if he can remember if it was liquid or powdered egg, but I'm sure it was powdered.
[edit]
He also showed me the tub the mixture was in. there was a lot of it pre-mixed, in a large tub which he dished out. I doubt they get many orders for omlette, so I can only assume it;s the same ass the mix for egg foo young etc.