Um...everyone calls him Lee. All the time. The only time the Rock part is ever even mentioned is when he's being formally introduced.

EDIT: Oh I see, your referring to how Gai doesn't use some kind of suffix like when everyone else talks to him. I don't see how that's going to even enter into the translation anyway, I've never know any translators to bother to differentiate somehow when a character says -san or -kun etc. I'm not even sure how they would without adding lots of extra words.