And indeed, there is. Here's the way:
The main trick: Configure your controls so that "Right-Shoulder Button" is also Acceleration. Once you've done that, the next thing to do is wrap a rubber band around so that the "R button" is kept pressed all the time while racing. If you have a car fast enough, then you can leave it running around the test course B-Spec style.
How to do: Grind until you have at least 4Million. We need this amount to purchase a supercharged car, any lesser car will not do the trick. Disable Autosave. Race a bit more and regularly check the Dealers to find cars that costs 3.5M or 4M credits. BEFORE YOU BUY, SAVE FIRST. This way if you don't like the car you bought, or if isn't fast enough, then you can always press Home, bail out, and restart the game. So anyway, I tested several very nice race cars (those that costs 1M, 2M, 3.5M) and raced at Test Course to see if they were fast. If your car is too fast, you'd end up racing with F1 cars and that isn't good, since you'd just lose.
I found one car that will do this trick: PESCAROLO C60 HYBRIDE RACE CAR '05
There might also be any other car that will perform good which I haven't tested yet, but for the sake of this thread, let's stick to my chosen car. Anyway, if you have this car, race at S Rank for 99 laps (Test Course). It will reward you a whopping 1,071,000 cash in 3hours and 5 minutes of racing. The car was so good that it was ahead of the other 3 Escudos for more than a lap.
Car's Behavior: It will run reaching a maximum speed of around 378km/h and just slows down at every cornering (305km/h) because of the drag. But there's nothing to worry about. I raced againts Suzuki Escudo and they were slow like turtles compared to my machine.
Go watch TV, do your school homework or household chores. After 3 hours, smile at your 1 Million cash. ENJOY!