Is there a way to enable aero peek on the Windows 7 classic theme?
No, theres no way at all. Windows Classic uses a different graphics engine than aero.
Just some of my own commentary, and from my own experience, aero and basic/classic aren't too different fps wise. I would advise to stay on at least basic, if not just staying with aero. If the looks of aero is your problem, I'm sure there are some themes on deviant art you might like. Just a little something extra with my answer.
Use this DWM Theme which emulates the old ClassicTheme: