Agree with others in that:
1. You'd definitely be on the DNR list after this rental. And with many agencies being tied together in some shape or form, you'd then be prevented from renting from multiple agencies.
2. What would the reasoning be, other than to waste gas/time/money and devalue a car for no reason?
3. With maintenance that needs to be done, you'd need to schedule significant downtime and won't get anywhere near your desired number.

With the need for routine MX (tires, fluid changes [oil, power steering and possibly others depending on the starting mileage], oil filter, fuel filter, air filter, etc). I'd imagine that:
1. The rental agency would never reimburse you for these if you pay for them and try to get reimbursed after so many miles
2. If you fail to have the mx done, they can come after you for negligence as everyone knows cars need work to remain safe/road worthy
3. If you try to swap out the car anywhere along the way for maintenance, they'll probably prevent you from actually swapping it and tell you to go find another way to continue your journey.