Auto Populate SubInvoices by cost code within New Prime Invoice

After entering all of my sub invoices for the current period. Having to 'manually' reenter these costs by cost code division with a new prime invoice is double work when all of this information exists. It would be nice to be able to have a drop down when creating a new prime invoice under each cost code where a check box can be toggled to include a sub invoice (sorted by recent date) already associated with that cost code. A few additional blank rows where custom value(s) can be also added would also be important. Having the subinvoice # identifier and/or the entity's name in this drop down list would also be helpful.

Attached is a mocked up example of what I am envisioning.