In Australia, they're not fog lights - they are driving lights and only come on with high beam. Weird that they'd wire them, differently between local (US) version and export.
I actually changed mine so that they come on with parkers and stay on from then if the manual switch is pressed - but I used a relay and all new wiring to achieve this. I then reused the factory circuit to power a set of driving lights behind the grill.
For your situation, my guess is that there are 2 relays - one that enables them to come on with the fog light switch, and a second relay that stops power, or ground, when high beam is activated. The easiest way to check this is to intercept the ground wire at the light (T into it with another wire), and have that go directly to ground. I'd just do one light as a test and if the light then works on high beam, you're done (well, apart from repeating on the other light).
If not, then it must be a powered switch that turns off the foglight relay when high beam is on - you just need to find that relay and trigger wire (pin 86) and snip it and tape it to isolate it. Knowing Ford - it's a ground wire switch though, so I'd try that first.
Sorry, I can't be more helpful.