Worldbuilder: promotion available on turn 0?

Is it possible to create a worldbuilder scenario in which I create a unit that starts with a promotion available? I can create a unit and set it to have enough exp for its first promotion, but the game doesn't seem to actually unlock the promotions until the unit engages in a battle. ANd I don't want to give it a pre-existing promotion because I want the player to be able to chose which promotion they want. I want to create a scenario in which the unit exists and can take a promotion on the first turn (as if it had just completed a battle or had been created in a city with a barracks).

Is this possible? If so, how do I do it?