The_Unbeliever
Honorary Master
You can try this:
1. Make sure the lifted side of the car is properly supported (no, not on a jack!)
2. Get a mate to sit on his ass with his feet pushing against the undercarriage/suspension while puling hard on the wheel towards him (or the nut) with both hands.
3. While he is pulling hard you try and untorque/loosen the nut. The outward force exerted by the rim on the nut from your mate pulling might just help in it catching some thread. If never done this on something this big but it has worked many times before on slightly smaller things.
If you can pry something in between the rim & hum and apply pressure that way you might also come right. or if you can get a hydraulic jack between the rim & chassis somehow and try to apply pressure that way.
This.