Oh I wish I lived near you I would come and help you.

This may seem harsh but if you can manage to get Beastie into your home, at the right sort of time, this may take a few days to establish a routine, say always putting some food in your kitchen at 6pm, or whatever time is best for you and Beasties visits. Once he is in you have to coax him away from the door, again may take a day or two.
Have a large towel near your back door.
Once he comes in and is far enough away from the door, close the door, quietly and carefully, pretending not to be interested in what Beastie is doing.
Let him have his meal.
Then catch him in the large towel, this is quite hard and hold him in it, making his only route out the kittie box!!
Or cat trap, from a cat charity!