OAF - Is this possible?

We have a descriptive flexfield on an OAF form and it currently has an associated value set.  This username field is displayed on a create supplier form and on a supplier inquiry form.  We only show this field if the supplier is also an employee.  On the create form, when the user searches for the username, we want to only display a list of names that aren't already a supplier.  However, on the inquiry form when they search username we want to only display a list of employees that are suppliers. Mainly, the goal is to prevent a username being