How to Sync HR and FND User Email Addresses?

Posting here because there will be more visibility here and the issue partially falls under HR.

We have number of users (in the 1000's) where the Employee (People For> Office Details>Email) does not match the FND User Email address. We want the email from the People form to be reflected on FND User form.

Ran the WF User Role Validation program but it did not help

There is a new WF process to synch the email addresses in 12.2.9 but we are on 12.2.8.

What's the easiest way to synch the email addresses? a simple update statement would do but it's hard to convince the client.