Samuel,
Well, let me start by saying that I have never actually tried this! However, SAP online help implies that it is possible.
You would need two PA groups, and two PA procedures. One would be for the FGs and one for the components. The Component group can only contain the two characteristics RULE_MATNR and RULE_WERKS, and no other characteristics can be checked at the component level.
I would imagine that you would then enter the FGs procedure into the FGs product master, and the Component procedure into the Component Product Master. The check instructions for the components should be allocation first; then product check. Here is where I have no experience combining the two distinct checks, but you should be able to set up a test proof of concept in your sandbox in a few hours.
Online help for MATP (where it speaks of component allocation)
http://help.sap.com/saphelp_scm70/helpdata/EN/05/7e1f3bc779144ae10000000a114084/frameset.htm
Look down the page to the section entitled "Mapping of capacities using product allocations"
I suggest (as always) that when you create such solutions, you need to create them one at a time; and ensure that each individual solution works flawlessly on its own before attempting to combine them:
1. Configure and Debug MATP without component allocation
2. Configure and Debug MATP with component allocation
3. Turn off MATP; configure and debug FGs PAL
3. Turn on all functionalities and debug the combined solution.
Please let me know the results of your findings, I have always wanted to try this but never had the time outside of my regular project work to set this up.
Best regards,
DB49