Commitment Question

Good morning -  need some help with this particular scenario. 

Client is starting to use multi-packs and the pickslip is committing partial quantities to locations that do not have sufficient quantities.

For example:     Item is sold in ea. and pallets. The pallet quantity is 40 ea. Some locations have 40 or more while others have less than 40 ea.

                          The sales order is entered for 3 pallets. They have 80 ea. In 1 location and other locations with less than 40 ea.

                          They would like for the pick slip to commit 2 pallets and backorder 1 pallet, since the remaining quantity isn't available in a single location to create a full pallet, even though the other locations combined have enough inventory to fill the order,