combining friction shifting with indexed components I would like to combine friction shifting and a 7 speed freewheel with current Campy Chorus derailleurs. It seems to me that the way that friction shifting works would allow this combination, since all that happens is that tension on the cable adjusted manually to get the derailleur to move between chainrings, right?

Is there any feature of indexed operation that makes this unlikely?
Yeah, the only real problem is maintaining fine enough control of the motion, both in actively moving the lever, and in avoiding "creep" between shifts.  In part it comes down to how much fine muscle control you have, and in part it has to do with the quality of the shifter and how it's mounted.