Want to change the ownership of a subsite to a different user

I have a multisite with many subsites. I have one user who has two subsites, and I would like to transfer one of their sites to a different user (who is not currently a user).

What's the easiest way to do this? I know you can't do in from the WP admin area, but what about going into the database and changing the user there? The new site owner does not yet have a username, so should I first create the new user and then go into the database to change the user for that particular subsite?

Or is there a better way? Of course, after the new user takes over that site, they can change the password.

I am using Prosites. I know you can transfer Prosite status to another blog ID site, but I would rather not create a new site.

Thanks, Joe.