Not too late at all. But establish the trellis framework so you have something ready to tie it to before the growth comes.

Thanks @yardvaark! Have you ever seen anyone lop it off all together in the spring to get branches down low?

Quite a few times I have cut woody plants to make them sprout new trunks. I see a tag. With a new plant, you'd probably be better off letting it gain strength, develop more roots during the cool season and lopping off before spring growth. But have the espalier frame installed before you lop as the return growth will come quickly.

I wouldn't prune it. I would install a simple trellis behind it, which could possibly be attached to the fence with offsets. After doing that, I would arch those two more upright branches over into a horizontal position, so they are parallel to the two branches you already have in place.