Bedroom pier unit assembly

I have this pier unit that is almost assembled. It came with no instructions.

There are the two piers, and a bridge, that slots onto a "T" shaped fitting on each pier.
On the bottom of the bridge is a slot.

On the top of the headboard is another slot.

There are two mirrors, and a vertical wood piece, which mount into these slots.

What I'm not seeing, is how to get the mirrors and the wood into position, holding each with one hand, while putting the bridge on with my other two hands.

Is there a trick to this?
HELP!

Without a photo, I'm having a hard time visualizing this.....if you can't get a helper, than what I normally do in such an instance is assemble everything on flat on the floor and then stand it up afterwards.