Hi Jobi,
I am quite sure this check can not be done. Availability Check is only done in the first level, so it only check the FERT.
I would need to understand your buiness process, depending on the time in which you create your orders, you can define a business process to deal with this requirement. E.g.: if your manufacturing plant ensure that 2 weeks of the production plan are frozen and only in these 2 weeks they ensure that only FERT materials without any missing material are scheduled, then you will be able to trust in the availability that you do for the FERT.
I hope this helps.
Thanks and Regards,
Mariano