In preparing for a running relay you have to prepare for the physical challenge of running but also for the non-running aspects of the race. Here are some things to consider adding to your training plan.
Set your alarm to go off every 30 minutes at night in order to train your body how to fall asleep and then be jarred back into the reality that it's a race and you won't get to sleep. To add to the effect place a light above your head that comes on every time the alarm goes off as if simulating the dome light of a car. If possible record the sound of car doors slamming shut and set them to your ring tone.
Go to your local track set out to run 4-6 miles. After each mile stop and consume real food items such as pancakes, eggs, bacon, cheese burgers or even your favorite treats. Training like this will allow you to roll through any nearby McDonald's during your legs to refuel. Much cheaper than gels or other typical runners food.
Immediately after completing a run climb into a large ice chest. Not as an ice bath treatment but rather to simulate the cramped space feeling you will experience after a run when it's time to climb back into your van.