There doesn't seem to be anything in the Gameplay Constants so I think you would have to do it with triggers. If, Then, Else would be the easiest.
Events:
Map initialization
Conitions:
Actions:
IF - (Race of Player 1 (Red)) Equal to Human
THEN - Unit - Create 1 (human starting unit) for Player 1 (Red) at Player 1 (Red) Start Location
ELSE -