If you open up the steering column, on the lighting stalk you'll see a wire harness with two distinct green/orange wires. One of those is the right turn signal, and one is for the fog lights. If you're looking at the harness from the driver's seat with it plugged in to the stalk, it's the green/orange wire on the very left you want.
All you need to do is cut the wire and ground the end coming from the harness and you'll get independent control.
Or you can go all out like I did with a SPDT relay under the dash and a switch so I can switch the fogs between independent control and the default headlight linked control...