It was a strangely worded line. Maybe, "Ahead full thrusters," or something like that. Maybe even shouting, "Ahead FULL THRUSTERS!"
Or no words at all, just an approving nod.
As far as Kirk having any kind of line like "engage," goes, he did say, "Take us home, Sulu," in the film. That's a line I can remember him using variations of more than once in TOS and the movies.