More flexible TASK lines?

I wonder if anyone else faces this problem:

I generally track my billable time for individual projects - for example, a complete print and broadcast campaign - and then use that as BASE INFORMATION for my eventual billing. It's very rare that I don't shave back some hours here or there or round a total dollar number downward in favor of the client, for instance, when he's someone you do ongoing business with. I feel now that I'm "trapped" with the line items I've entered as my guide.

Is there a way to create a means by which you can show ACTUAL BILLABLE HOURS in a different column from, say, "INVOICED AMOUNT"? This way you would have a record of the specific hours spent on all aspects of the project as well as the amount you actually billed. (Example - ACTUAL BILLABLE HOURS: $4518. INVOICED AMOUNT: $4500)

Along those same lines: Let's say you have a line by line task tally down to 7/7/06, then a place where it says "AMOUNT INVOICED 7/8/06," and then the tally starts over again. That way one project can have continuous tracking with multiple points at which you can invoice.

Does that make any sense?