What does your grey like eating most,It may be pine nuts,almonds,cheese,these are treats that you can use to gain his trust.I think it can be done but may take time.If you can,let him out of the cage and tempt him back in with a favourite treat.I see nothing wrong with him looking out the window.Place a stand there for him to perch on. Will he step up on to a stick,this may prove better for him at the moment and then gradually you can move your hand closer to him.For now be content with talking to him and giving him the treats untill he is happy with you doing that and then you can take things a step forward. It is not going to happen over night and may take weeks but it will be worth it.