Leave them in space III
Well (as someone who has had the pleasure of working with the Shuttles in the past) as said before, the shuttles aren't equipped for onorbit resupply. Besides crew consumables, there are the cryogenics for fuel cells, hydrazine for thrusters and OMS. It might be possible to work out some method to do so, but currently there is no ability. If I remember correctly the tanks assume 1G for tanking, so it might not work.
Orbits: The shuttles would have to be placed in high enough orbits so they wouldn't reenter and burn up after a couple of years. The ISS orbit is too low for this, that's why it requires periodic reboosts. Hubble's orbit is high enough, and certainly the shuttles can make it that high as a shuttle was used to place it there in the first place... Something to keep in mind is that NEO (Near Earth Orbit) isn't a benign place. Highly reactive monatomic Oxygen and Hydrogen are constantly attacking surfaces, as well as micrometeorites and space junk. Satellites intended to stay aloft for a long time are better protected to such then the shuttles, so the vehicles may not be terribly useful after a couple of years on orbit.
An interesting idea nonetheless...