One Time Data Entry In the Portal

Hi,

Is there a way to setup a workflow in the portal so that a user can enter data in a one off scenario?

 We have several thousand AD users and several thousand users in our HR system, however there isn't a unique key to link them. One method we're thinking of is importing users from our HR database into the MV, then import users from AD and perform a join on givenName, sname and mail. Once we have the join we'd then like to push an employee ID number from the HR DB to AD and use that as a unique match.

 We want to allow users the ability to enter their employee no. in the FIM portal as a one off exercise, is it possible to allow a user to enter data for a particular attribute only once?

Thanks