Well, I really thought you were in a mess here. But, after looking at the wiring diagram it would be rather easy. The fog lites come right off the light switch through fuse 8. They do not go through the Exterior Lamp Module as all other lights do.
There are no term 15 (switched hot) positions on the light switch so I would disconnect it and find a suitable term 15 to power it. If removed at the light switch the fuse will be between the wire and the lights, protect your insertion.
Bosch Master, ASE Master, L1
33 years MB technician