There is no possibility to reverse a hashed string back to the original string. If you found a service which offers that, they using rainbow tables. See http://md5.gromweb.com/. For this reason there is no reverse function inside the saltedpassword extension.
You also should ask yourself why you wanna show the user the password. This will put your extension into a bad light security wise. As a user I would think that you save my password as plain text into the database.
But to answer your question: You can of course save the plain password in the session and print it at the end of registration process.