The dealers don't offer that, the manufacturer does. It's a salesman's nightmare.
Look at it this way dude; we get paid on commission. We understand that there is a certain percentage of people that come in for joyrides and/or just to check cars out with no intention of buying. We also understand that there's nothing we can do about it.
All we ask in return is that you are respectful of our product and our time. What is the purpose of your visit? To get $50. And, obviously, to joyride a V8 Mustang. That's pretty disrespectful.
You work at Autozone or Advance Auto or something right? How would you feel if you had a guy come in and ask you to move a bunch of heavy shit around, bring it down off high shelves, install it on his car just for him to see if he likes it, and then just have him say "nope, not for me" and drive off, leaving you to clean up the mess he made you create? You'd do it because it's your job, but you'd probably agree that guy is a douchebag.
That is you, if you go in and demand to drive a V8 Mustang with no intention of doing anything other than collecting $50.