John:
You have come across the reason that most organizations with a large resource base do not import timesheets. There is no nifty way to adjust them programatically in an On Demand system. If you do not have a lot of them, then you can have an administrator (or the resource manager) enter the adjustment. It is a pain, but if they are not common, it can be manageable. Even those that are using an interface to an Agile system end up creating the Adjustment directly inside of Clarity...and by the nature of how Agile projects are run, the need for Adjustments is very low.
Most organizations that are importing time from external systems bring it in through Transaction Entry. Using that method, you have the option of the detailed day-by-day transaction import, or you can summarize and bring in only the weekly totals. And, if there is a change (adjustment) in the time-keeping system of record, the transaction entry import process allows you to enter negative numbers so that you can have it handle the adjustment and provide a full record of the change.
To use Transaction Entry, you will need to have at least a minimal financial enablement, but that is normally easily done if you are not using the rest of the functionality. Default values are sufficient for a minimalist set-up, and can be done in an afternoon.