How to select specific contract line during draft invoice generation

We have a use case, where customer has issues a PO with multiple PO lines with specific funding. We are creating each PO as a separate Contract and PO lines as contract lines. Based on the WBS structure, each contract line need to be associated with same project and a task. We are not capturing contract and line ID as a part of Project Cost Import.

There is a need to generate a draft invoice using a specific contract line, so that Funding consumption can be tracked by appropriate contract line. Also, there is a possibility of using both the contract lines in a single invoice.