Hi Nicholas,
I don't have a sure solution for you. But based on what we did in Oracle, I think you can do it in SQL Server this way,
1. Export user name and password_hash information from sys.sql_logins system view to a text file.
2. Run CREATE LOGIN <loginName> WITH PASSWORD = <hashed_password> HASHED <other options>, where the loginName is a user name from the text file, the hashed_password is the associated hashed code.
Hopefully this is what you are looking for. Thanks!