That's also something I am looking for.
I have a 3 month project that is being billed in increments. One at the start, then again at 30, 60 and 90 days. Each invoice is a percentage of the total project.
It would be great to have a fixed cost project, then, when creating the invoice, I can specify an amount to bill against that project.
Right now, I have to create 4 different fixed cost projects, add a single time entry, mark the project complete, and the create the invoice.
I would like to be able to create an invoice for a fixed cost project, not requiring any time entries, and also be able to choose the amount to bill (partial, full, or remainder).
Greg