I think it would be hard to do. I would have so many reservations about it. But at the same time, Paul was so eminently respected in the Christian world, Philemon might have been happy to obey this request of Paul's.
Today we come to the last couple of verses:
21 Confident of your obedience, I write to you, knowing that you will do even more than I say. 22At the same time, prepare a guest room for me, for I am hoping that through your prayers I will be graciously given to you.
23 Epaphras, my fellow prisoner in Christ Jesus, sends greetings to you, 24and so do Mark, Aristarchus, Demas, and Luke, my fellow workers.
25 The grace of the Lord Jesus Christ be with your spirit.
Paul was confident that Philemon would be obedient to this asking, and even do more than he asked. Makes me wonder if Paul expected Philemon to not just welcome Onesimus back but if he hoped that Philemon would once again make Onesimus part of his household. But those are just wonderings. :)We should as believers welcome new believers into our lives, our households, our churches. Not drive them away because of what used to bes. But to see them as the useful people they now are. Useful to God himself.
The last two verses are standard closings for Paul. He extends greetings and prays a blessing on him. "the grace of the Lord be with your spirit."