Personally I feel you are expecting a bit much from the dealer by asking them to replace an alloy.
Yes they are liable for the damage and should be putting it right and they have attempted to do that by contracting in a wheel refurb company at their expense.
It's unfortunate that the quality was poor, and you are right to ask for it to be rectified, but this isn't the dealers fault.
You should be pursuing the wheel refurbishment company to source a new alloy and replace the tyre for their poor work and mis-use of the vehicle without permission (I'd be asking for at least a fuel contribution on that one).
If you contact the finance company they probably won't get involved as the car is mechanically sound and the dealer has attempted to put it right, but the repair quality is out of their hands. If the car had mechanical issues or was unsafe then you would probably have their full support, but for a damaged alloy and tyre by a 3rd party company, they probably won't waste their time.
Don't get me wrong, I fully support your efforts to get it rectified and I have been down this road myself this year when I rejected a brand new Focus ST with a Ford dealer. I just think you are fighting your battles with the wrong company.
Good luck though, I will keep an eye on this thread as i hope to see a decent outcome for you.