Hi Ruben,
You can add non stock item to production orders, but you have to provide the mandatory data required for external processing. Therefore you need to provide data like Material Group, GL account and purchasing group.
If you are using BAPi BAPI_ALM_ORDER_MAINTAIN there you will find the relevant fields in IT_COMPONENT. But this BAPI you might not be use for Production orders types.
Please make BDC or LSMW to add components in Production orders. BDC is easy option, there you can make dynamic BDC's in one program to handle all the scenarios related to Production order components.
Regards,
Amarnath Dube