Adding Default Values in Data Grid rows

Is there a way to add default values when inline adding rows to a grid detail?

I have a list page of contracts that maps to a form page for each one. This page contains a table of deliverables that are of course connected by  contract ID of the parent contract (Lookup column).

I understand how to add default value through a mini page, but how can I set default values when inline adding a row to a table with the "+ new" button at the bottom of every list?