Cut a couple of sticks about 3/4 to an inch thick, cross them at the appropriate level to form a bipod and tie them with a length of cord.
Now, why the heck are you hunting from a lean to since it probably cuts down on your field of view quite a bit and also reduces your ability to hear anything from the sides and rear? Just curious.

Coastie
"Children are tastier than Dogs or Goats and they're far easier for a Leopard to catch" Indian Magistrate Hari Prasad Tivari