Hi Jeremiah,
In addition to Narayan's suggestion, if the Task level date in question doesn't tend to change very often, another approach would be to create a custom date parameter on the Project itself (e.g. Target Date, or Primary Sorting Date), manually type that date in, and then sort your Project report on that custom data pararmeter.
Crude, but effective; and if worth it, automatable.
Regards,
Doug