I know there is other write-ups on this but I though I would share my experience...
you will need two buttons, a soldering iron, wire, a drill and twisty ties
this is the clicker I have
and these are the buttons i bought from radio shack
First take apart the clicker...these are the pegs you will need to solder to(highlighted in red)...I only used two of the three buttons but if you use the third then you would solder to the pegs highlighted in yellow.
once you solder your wires to the circuit board and solder the buttons secure the battery back in the clicker. I broke the clips on myne so I used zip ties to secure the remote to a piece of wood
mark and drill two holes for the buttons to go through-i took the button tops off to make for a sleeker look...also easier to get through the holes
next drill through the ash tray where you want the buttons to pertrude(i got impatient here and as you can see chipped the ashtray a little, slow it down and be careful
find a good place for the clicker to sit, i found some free space between the idrive nob and my center armrest
glue or tape the buttons securly to the backside of the ash tray or if you bought buttons that have nuts on them to tighten do that.
put everything back together and enjoy you new opener...