Can the stock tires be worn out? (perhaps a bit prematurely?)
I'm thinkin' you want to reduce rolling resistance as much as possible by eliminating the aggressive tread.
Make sure all of the bearings are really smooth......again, to reduce rolling resistance as much as possible.
Think light!
I'm not sure if aero will come into play too much, but I'd be tempted to explore a really lightweight body or fairings to take as much drag out of the equation as possible as well.
That's all I have off the top of my head..........it sounds like a fun project!