You don't have to use a pump to fill the diff. It's a pain, but you can do it using the quart bottles of gear lube and a piece of hose. Cut the tip off of the cap of a quart, slip the hose over the nozzle on the cap, stick the other end of the hose into the diff, and squeeze the quart like crazy. Once the quart is about half empty, refill it from another quart, and keep going. If I need to explain this more clearly, let me know and I can give it a shot.
-Rod