Lawson EMPLOYEE number to Landmark ACTOR

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While working on one of my ISD (excel designer) report, one PfiWorkunitVariable variable is EMPLOYEE number. I would need to do a vlookup to the employee name. We are only using IPA in Landmark, everything else is still LSF. So we don't have the employee number in Landmark yet.

I am looking to store the employee number to the Actor CustomActorFields.UserString1 from Lawson Security Manage Identity-EMPLOYEE (Actor=RMID). Is there a better field than CustomActorFields.UserString1? Other than IPA/Processflow, is there another way to populate this field from Lawson Security?

Thanks