Tillering trees are nice because you can stand back and quickly assess the tiller, and if you set them up to replicate your shooting nuances, you can precisely balance the limbs relative to your holds.
You can make a tillering tree (rope and pulley system) on a 2x4 and then ratchet strap it to a pole or tree or put it in a bench vice, or trailer hitch, etc. It doesn't have to be mounted on a wall.