IF you are able to this is the best way,

take bamboo blinds like dutch lover said. cover the window so no one can see. Make sure to leave the window open a few inches. Then cut a piece of ply wood the size of the window. Cut a whole in the wood for the air duct.

Attach the plywood to the window and try to air seal it to the wall.
I saw a guy do it in a pro grow video.