how skilled are you at electrical?
if you are not very skilled at electrical this will not be easy to accomplish without some severe modifications or an added switch. then you would loose the fog lamp switch functionality. the smart junction box controls the ground side of the fog lamp relay by gnding the brown wire at the smart juction box; you could just wire a gnd side switch to this feed and disconnect it from the smart junction box, but that would disable the headlamp switch fog lamp control. you could bypass the sjb, except the sjb fog lamp input switch is a power (grey/violet) so you could use the fog lamp input switch power to feed a relay power, ground the other side of the coil, now you have a relay commanded by the factory head lamp switch. now connect one of the switched side of the relay to the brown wire at the sjb and the normally open contact of the relay to ground, cut the brown and grey/violett wires at the sjb and you should have factory switch controlled fog lamps in all positions. the sjb would be bypassed.
............ well in theory at least.