If you want to see the speed displayed on the MFD, you can set a speed warning and your speed will flash up there, but that's inefficient and it probably isn't exactly what you're looking for.
However, there is another trick, if and only if you have dual zone climate control. Hold the ECON button and at the same time, the button that makes the air blow UP. This will make the two screens that usually display the temperature, display some funky numbers. When you have this, turn the drivers side temperature to -19. Then, turn the middle dial 1 click to the right, so you should see -191 on the drivers side temperature. The passengers side temperature will show your speed. This number is actually a WHOLE lot more accurate than what the speedometer says, I checked it with GPS. Once you pass 100, the numbers start to blink.
It really isn't complicated to figure out, but if you don't understand it, I can post pictures of the step by step.