If you're doing a relay, you're basically doing a 40k TT. Treat it just like a bike-only TT, leave it all out there (do you do bike races?). I would advise you not to use the "arms hanging over the top" position on a road bike; if you're a decent cyclist, you will be passing many people and it's hard to react quickly in that position if you need to dodge someone or brake.

Practice the course, do long intervals, go have fun.