Your not
going to like this....to get to the three plugs in the back you have to
put a jack up the car, put jack stands under the front of the car, then
you take the jack put a piece of wood on it so you dont damage the oil
pan, raise the jack under the engine just enough to take the pressure
off the engine mounts. Then you have to unbolt and remove the engine
mounts, then lower the jack. now the engine will be low enough so you
can access the rear plugs.
RECOMMENDATION...If I were you since changing
the plugs on this car is such a pain I would spend a few extra dollars
and get the pre-gapped Bosch Platinum 4 prong spark plugs, they last
the life of the vehicle and never have to be re-gapped. This way as painful as changing them is, you will NEVER have to do it again.
Otherwise, all you need it a Flexible adapter that can connects to your extension and you can add extensions and reach them from the top..
Still not easy but reachable.
Let me know how this works out for you.
Benjamin