Can the Space Shuttle tow orbiting cargo to the space sta

Since it looks like there may be a gap in American access to the ISS when the shuttle retires, and before Orion is ready for launch, and America can't buy seats on the Russian Soyuz craft, is it possible to trade cargo delivery to the space station for American seats on the Soyuz?
This trade has been done in the past, but today, we don't have any extra room on the shuttle to carry any more than our already agreed upon payloads. We also don't have any unmanned space vehicles capable of rendezvous with the ISS. If the U.S. were to attach consumables to an already existant commercial satellite bus, launch that bus using one of our other rockets, then meet up with, and grapple it, in orbit, with the robotic arm on the shuttle, could we tow it to the ISS?
This would allow the U.S. to retire the shuttle on time and free up money to complete Orion without losing access to the space station for American astronauts.

Do the shuttles carry enough RCS fuel to move that much extra mass?

Can the robotic arm handle that kind of load?

Is the shuttle capable of docking with the station with that much extra mass attached?

Is there some important limitation that i'm missing here?

there's no way. the shuttle doesn't/can't carry nearly enough extra fuel for such a maneuver, and most satellite launches are full, or near enough, already anyways. now you MIGHT be able to launch a package into a close orbit then pick it up and deliver but that seems awfully iffy. my inclination would be it would cost way more than just buying a soyuz launch, especially since it involves the shuttle.