collective Billing

Hello,

we have F2 billing for sales order and FV billing for contract, both are order related billing.

Client want to combine Sales order and contract in SINGLE billing document but without changing billing document type. How can we do that.

e.g.

Sales order 1 ----- billing type F2

Contract - 2   ----- billing type FV

Create billing (doesnt matter billing document type) which will include Sales order and Contract.

Thanks a lot in advance.

Vishal