How can I plan in this scenario

 Hi All,I have the following scenario:

 Item A is a purchased part and sourced from multiple vendors based on sourcing allocation percentages.

Item A uses Item B which is supplied to the respective vendors.

Item B is drop shipped to vendors location (supplier for Item A) based on PO Qty for Item A

In this scenario how to plan the requirement for B considering MRP will not explode beyond A since that is a Buy part. Also if we make A as a "Make' Item (with B reporting to it), then we will most likely need to create separate orgs (per vendor) in order to source A based on allocation percentages.