Wear and tear aside, there are a couple of issues as I see it.... but the laws could be different over there to here in oz...
Usually a domestic vehicle warranty will state specifically something like "if the car is used for PRIVATE purposes only" or similar.
(Beyond that, you'd need to be a lawyer to argue the point, and a judge to actually decide if it is the case or not)
Here in Oz, another big danger (maybe even bigger than warranty) would be your insurance and registration. That is paid usually on a private or business basis. If you are using it for business purposes (for your job) the insurance companies COULD refuse to honour any policies you acquired for private use ONLY!
I'd look into it in detail BEFORE I used the car for that purpose.
That's my advice anyhow. I'd be VERY careful.