Inter unit Billing using Contract and PC

I have unique question for Contract-PC-BI.

We are using inter unit billing(recurring) and is working fine.   The interunit template has  Interunit payable, interunit receivable, inter unit expense and inter unit revenue a/c.Users wants to use contract for each bill and send the transactions into PC.  .   Created a contract as Recurring with billing manages revenue as billing method.  The billable amount is driven from product. We are able to see  the billable amount in the bill plan. In contract, the revenue  chartfields are a/c, operating unit, project .

Ran CA to BI process and ran Billing interface. Bill is created.   Updated this bill as recurring bill with schedules, added operating unit  for inter unit expense side and saved. This becomes as template for recurring bill.   Operating unit for expense side are different for each customer bill.