SHIFTERS HAVE TO BE ON THE WHEEL!

Of course, how else would you be able to drive a real F1 car sometime? So let's get some of those wheel-based shifters.
First you'll need some resources. Two buttons, which fit nicely in the two outer or middle holes (one left and one right) on the steering wheel, preferably with the buttons located at the BACK of the wheel. You'll also need some wires. You know the kind of wires that connect your cd-player to your amplifier? (The black ones, you know!). Get a piece of this stuff, without connectors of course. This should be a double wire, each wire consisting of a shielding and an inner wire. About one meter will probably be more than enough, but remember: you can make wires shorter easily, but making them longer is much harder to achieve! Furthermore you'll need a soldering bolt, a boring machine and a steady hand!

When you've got all this, let's get to work.
First, mount the buttons in the wheel. The buttons should be located at the back of the wheel, for realism. If the buttons are a little bit too small for the holes, you can wrap them up in a bit of black isolation tape, and they will fit perfectly, no glueing required (if you've got the right buttons that is).
Next, remove the cover of the steering unit. It's secured with the six screws at the downside of the box. When you've removed the cover, you'll see mostly air, but also a bunch of wires. We only need three wires for our purpose: the yellow, the purple and the red one. The yellow one is the ground wire, the red one is the one for button #1 and the purple one is for button #2. Now you have to strip a little bit of each of the three wires. The wires are VERY thin, so I suggest you use your soldering bolt to melt a bit of the plastic to strip the wires, instead of using a knife or a pair of scissors or something.
Now, get your piece of audio-cable handy. Connect (using your soldering bolt) the shielding part of each of the two cables (it was double cable, remember!) to the yellow wire. Next, connect the inner parts of the two cables to the red and the purple cable respectively.
So now you have a piece of black double audio cable connected to three wires in your unit. This piece of cable has to come out of the unit! To fix this, drill a small hole between the two holes used by the two clamps. Get the cable through this hole, making sure it does not interfere with the steering mechanism at all!
Now you have to connect the wires to the buttons. Find a way to lead the cables to the buttons you like, making sure there is enough cable so there won't be any strain when turning the wheel to its extremes. Connect the button #1 wire to the right button (both the shielding wire and the inner wire, using the soldering bolt!) and the button #2 wire to the left button. You can use some black isolation tape for the finishing touch, connecting the cables to the wheel properly, etc. It's really neat stuff, this tape!
Make sure you feel comfortable with the result and that there's no strain at all at the points where the wires are connected to the buttons. Close the unit and take your new baby for a spin! Of course, I have to advise you to first test it before closing the box, but oh well.