Although moving a dog from paper training to outside training is not easy, it can be done. What you are going to need to do is slowly (and I mean slowly) move the paper closer and closer to the door. While you are doing that, also make the paper section a little smaller each time you move it. Eventually, you are going to move the paper out the door and into the yard. Praise-praise-praise everytime your dog does the right thing. Great jackpot treats when he is going outside. Then slowly completely delete the paper.

A dog with real separation anxiety is not always a good candidate for crate training. It sounds like you have done a terrific job with his SA. Putting him in a crate at this point might reverse the progress you have made. That being said - I am a big believer in crate training, but to the SA dog - it is not always an option. If you have a crate, however, you can see how he does in the crate with the door open. Many SA dogs like a crate as long as they are able to get out at will, because it makes them feel safe.

If he is doing well in the house except for the paper training, I would try the above exercise and see if you can get him to the point where he will only go outside.

Good Luck!!