You should be able to do this using the entry points for the preparatioh list generation.  You would have to generate 4GL code to use the entry point to check the PRECOD value.

You can use the AUTPRLFIL entry point

I think you should be able to use the formula that is available without using any code.  On the right hand panel in Prep Plan there is 'Preparation Plan Criteria' which you can interrogate the SORDER and SORDERP/Q tables...