I like where you are going with this. I too am looking to buy one (jumping from the Audi flagship) and go down a similar road.
I have thought about it a little and I think that you could have some delrin spacer blocks machined for spacing between the top of the struts and the body. I'd say a 1.5" to 2" block would get you enough room for a more appropriate off road type tire that would give you more traction and more rubber protecting your rims. Delrin or a UHMW type plastic can be sourced from any decent plastic shop and any machine shop could turn them down in short order.