Belt drive is different than chain drive because belts aren't as flexible laterally as chains are. While perfect alignment of sprockets is important, getting the two axles parallel is more important. If you've ever used a belt sander you've seen how moving one end of the adjustable roller can cause the belt to walk to one side or the other.

I do these adjustments trial and error, but I believe the belt moves toward the side that is father away as if trying to become tighter.

So since you can't move the crank, tweak the rear wheel to one side or the other and see if that causes the belt to float to center. Obviously the wheel will now be slightly off center in the chainstays, but it should only need to be a hair off.

As far as which way to face the hub sprocket goes, you want the direction that keeps the belt centered naturally with better wheel alignment in the frame.