As far as I know Mika the only way to access the back of the fog lamps, to change the bulbs on the post 2005 K12's is to remove the plastic inner wheel arch cover.
Hope that you have better luck with LED bulbs than I have had. All of the unbranded ones that I have tried have been great for a few weeks then failed.
Now trying these for the front sidelights.
If they last half of the 6 years that Osram claim for them I'll be happy