Customer Specific Lookup in Sales Order/Sales Order Invoice Data Entry

I am stuck and I think the following cannot be done so consider it a challenge to everyone to see if someone can come up with an answer that is not crazy complex.

I have an end user that would like to track who picks up Sales Orders...picture a field in Sales Order Entry called "Picked Up By:"  The catch is that they would like to have a list of who is authorized to pickup an Order that is Customer specific.  That means that at the Customer Maintenance level we would assign who could pick up an Order for that Customer...Joe/Sue/Paul for example.  Then, when the Sales Order is entered for that Customer we would see only Joe/Sue/Paul as our only choices for "Picked Up By:"  Also, Sales Order Invoice Entry would act the same.  It would work almost identical to a Ship To Address for a Customer where the list of choices is specific to the Customer.

Any ideas if this can be done without scripting?

Thanks!

Adam