if you know the pinout or (look it up) on the trailer connector you could probably get away with connecting a incandescent bulb the way like he does in the video, that simulates a load and should make it operate for testing, or just swing by a rental place that looks not busy and ask if you could plug in a trailer to test your controller.
if you look in the engine compartment at the front of the fuse box there is 2 post's there and each one should have a red wire attached, 1 is to power the controller and the other is to power a trailer.