Im doing this at the mo. Using a sparco mount with 2 buttons on already, will add the other 2 myself (from tweaks) The problem is they aren't normal switches, they use a resistor to show a resistance to the ECU. You need 910, 275 and 100 ohm resistors, the other is a straight switch so no resistance.
I'll do a guide as I go through it, waiting for the mount to be delivered at the mo.
ETA: or you can use the OEM board but I wanted it cleaner.