How about a pvc pipe feeder that goes through the left wall with the window and upwards so that you can fill it from the outside and it can still be under the roost inside. I'm thinking outside the box here a bit and I've never done this so I don't know if it would work but I saw some designs for systems like this. Search on PVC pipe feeders. I think one of the crucial things was to get the angle in the elbow less than 90 degrees so that the feed flows freely.
Hope this helps a bit.
Hope this helps a bit.