Our solution using Collective Process Orders needs some help

I am in the Paint industry.  We want to use Collective Orders but are facing a snag 25% of the time.  Can you please offer suggestions?

We make a BULK batch under a Process Order and then fill it into various types of packages (FERTs) under one or more Process Orders.

The BULK is made in batch sizes of either 500, 1000, 2000, 3000 or 5000 gallons.  At the time we create a BULK Process Order we know exactly in which packaging sizes / quantities it is destined.  This is why collective orders work so well.  We can use the automatic goods movements between the two levels of process orders because we really don't need to hold the BULK in inventory.  Additionally, collective orders offer excellent scheduling functionality, such that when the BULK process order is rescheduled the FERT process order is rescheduled automatically; in other words, both the FERT and BULK process orders are kept in sync.

75% of the time the relationship between the FERT and the BULK is 1:1 so collective orders work fine.

However, about 25% of the time we make two or even three FERTs from the one batch of BULK.  I don't think it is possible to have collective orders where there is more than one FERT for a given BULK.  (The other way around is normal/common).

When we make two or three FERTs from one batch of BULK it is not always the same two or three FERTs, so co-products is out of the question because the possible combination of FERTS would result in too many co-product items on the BOM.  Also, the two or three FERTs are often run on completely different packaging lines.

Any ideas?  Thank you very much.