How to setup an external User Defined program for Eligibility Testing

The P08390 / W08390A program/form allows for entering one ore more eligibility testing criterias in the grid located in the center section of this form. But this form also allows for entering the name of an Eligibility Testing User Defined program in the event that the methods offered in the grid for eligibility testing (Method* , field MTHD) (AM, AX D, H, M or Y) do not suit organization's requirements.

Then my question is: Provided that we enter the name of an external program written by the IT department, that is to be called to execute a special eligibility routine if none of the predefined Methods AM, AX, D, M, Y or H available from the grid are suitable for eligibility testing,