Purchased Part Within a BOM - With Free issue Manufactured Parts

Hi All,

We have a Purchased part (Part A) that we buy from a supplier that contains two pieces (B and C) of "Free issue Stock" from ourselves.
Part B is a manufactured Part and C a purchased Part.

Part A will be a stocked part as well as appearing within other BOMs.

Part B and C are stocked in a warehouse at the suppliers premises (but is regarded as our stock and is in our warehouse). We will maintain the stock of these via MRP.

I need parts B and C backflushed when Part A is used within a BOM or we require stock of part A.

Although I can get this working in some fashion via sub-contract when pull as assembly This really isn't an option as I need the part to be pulleed as material.

Does any one else do this or have any ideas?