OK. Pull the fog light switch out of the dash. Looking at the back of the switch, there are 5 wires that go into it. The bottom two should be the same color scheme. The very bottom one is a permanent ground wire for the switch. The next one up is +12 volts when the high beams are on, but a ground otherwise. If you want your highbeams to have no effect on the fogs, cut that wire. Cap the side coming from the wiring harness. Connect the stub on the switch to a ground. It can be connected with the other ground wire no problem.
I did it on my car. I also did the parking/fog mod, but I screwed up and grabbed a +12v supply that was controlled by the damned dimmer, so if I dim the dash lights my fogs turn off

and I haven't bothered to crack the dash again to fix it.
Use a test light to verify that your wires are the same as mine.
MY01 RS