I'd try to negotiate with Cornell. Might be worth going there in person. If not, your scheme of starting at Tufts and transferring seems reasonable. If you worry about lame peers, take upper-level courses as a freshman. Audit them if they won't let you register because of prerequisites. I suspect most profs would even grade your work in a case like that, so you'd get the full intellectual benefit of the class, just not the credit.