Item category with delivery - NO PGI - Invoice

The requirement is as below:

The material is a BOM material. The pricing has to be only at the main item level (dummy material - not relevant for stock). The sub-items will go to delivery and PGI and not relevant for invoice. Only the main material will go to invoice.

Below is the setting i have maintained at item category level:

Item category Billing Relevance
Main item B (Relevant for order-related billing - status acc.to order qty)
Sub item Blank (not relevant for billing)

Problem:
The invoice for the main material gets created even if the PGI of the sub-items is not done. i.e. there is no check before invoicing if the sub-items are PGIed or not. In other words, what is the item category setting to bring an item to delivery and NO PGI and then invoice.

Please let me know how do i handle this scenario.

Thanks,
Shan