Did you get the CSL Supplement with your manual? Because the oil level sensor is specific to the CSL, it's in there.
If you didn't get the supplement, here's the procedure out of mine:
Quick Measurement
If necessary, the current oil level can also be measured quickly. for example after the oil has been topped up, but you should bear in mind that such quick measurements are less accurate:
1. Position the car on a flat, level surface.
2. Switch off the engine, which should be at its regular operating temperature.
3. View the oil level reading on the onboard computer, see page 12.
4. Start the engine and allow it to idle for at least 2 minutes.
5. Press and hold down the Sport button, see page 11. The reading for the current oil level flashes on the display.
If the old long-term reading appears instead of a flashing reading, the system was unable to perform quick measurement. This can happen if the engine temperature is too low, for example, or if the car is not standing level. A line of dashes in the display indicates that measurement is still in progress.
Which is, er, basically what you just said!
