I've tried many methods, but the shooting rail on my newestladder stand has provided the best option yet. I can put the butt of the stock on the seat beside me and the riser sets on the rail. Very little movement to pick it up, and it's already oriented in a position to shoulder it.
I have used tree steps, accessory hooks, etc. but I always have the naggingthought of what could/would happen if it fell. A loaded crossbow hitting the ground pointin up toward the stand could get ugly! One option is to use a short "tether" made from an old "pull-up" rope to give you room to shoulder & shoot, but attached to the butt stock of thebow (rear sling swivel)so it couldn't hit the ground if it were accidently dropped but would be pointing down when it jerked to a stop. Never dropped one yet, but the possibility is always there!