Big question is, where did the nail puncture the tire? If it was in the tread area you can certainly patch this yourself with any tire plug kit for very minimal cost. If it was the dealer that told you they couldn't patch then you got taken for a ride. Of course they will tell you to buy a new tire as there is a tremendous mark up on new rubber. Any local shop should plug it for you and you should feel confident the plug will probably outlast the tire.
If the damage was in the sidewall then yes, it needs to be replaced but this is the same for tire, RFT or not.
I keep a similar kit in the wife's X3 for this very scenario:
http://www.amazon.com/Slime-1034-A-T...uct/B000ET525K