My parents had to co sign for a loan when I got my 00 Z28. I refied 1.5 years later for a better rate and was able to do that on my own. Whan you have your meeting with your parents and the FA, bring it up that this could be short term and just to establish a credit history.
Another thing to think about to if this doesn't work out for you...
My favorite car is a 1997 Camaro SS convertible 30th Anniversary Edition, Artic White with Hugger Orange strips, LT4, 6 speed manual transmission, and the houndstooth interior. I want one of those really bad! I feel it would bring me complete happiness. Cars I own currently are a 1957 Chevrolet 210, a 1971 Corvette Stingray, a 1990 Z71 reg. cab sportside with 6" lift and 33" tires, my 00 Z28 T-tops and A4, and a 2005 2500HD Duramax/Allison CrewCab Shortbed 4x4. There have been times when I could have bought my dream car (haven't found one exactly like it, missing the LT4, but I wouldn't complain if it was the LT1) but chose not to mainly for the fact that it is always better for me to think and dream about possibly owning my dream car one day than it is to actually own it and see it get rock chips, sratches from unappreciative people, some stupid broad coming in off the freeway cutting across 3 lanes of traffic to hit the right rear wheel... I really hope that you are able to get the car of your dreams! I remember the way I felt when I got the Z28, but not getting it is not the end of the world either. Do what you can to get the deal worked out. If it DOESN'T work out, it is for a reason. Something else is bound to come through for you and it could be better...