Only show missing data in a form - insert not update?

Larry's Friday Girl

    This is kind of an odd requirement - the client wants the users to be able to fill in missing values for data loaded against employees in PBCS, but to be only able to input data into missing fields - these are smart list driven - not be able to update data already populated.

     

    Is this at all possible?

     

    Any suggestions including workarounds considered.