You would need to modify the wiring harness and connect the high beam leads to the fog lamps, incorporating diodes (with sufficient current capacity and low voltage drop) to prevent lighting the high beams when the fog lamps were used with low beam.
The question, though, is WHY? If you're using the high beams, the fog lamps won't help anything; they're for when you need to light a broad swath at very short distances (like in the fog, for instance), while the high beams are for high-speed, long-distance lighting.