Tie PO's or commitments to master budgeted contract

I have a master contract that I put into the Contracts - Budgeted section of CM 13.1.  I have 4 separate portions of the master contract, that have their own line items.  I want to administer these sub-contracts as separate entities, and when I update them each month, have those resulting numbers roll up back into the master contract.

Is there a way to tie entries into Contracts - Committed, or Purchase Orders to the master contract in the Budgeted tab?