V8

I've created a contract and want to track all Costs & Revenues over its life.

Sales, Expenses and Timesheets are all configured and when coded to the relevant analytic report correctly.

But how do I account for any replacement product costs? Creating a 0 value sales order or  invoice containing the replaced products and coded to the correct analytic account does not minus the products cost price from the total when viewing Costs & Revenues against the same contract.

Does anyone know of a community / paid for module that offers this functionality?