Some big CO2 tanks include a liquid out post for high volume dispensing applications. Whether your does or not is hard to say without details on or pictures of the tank. They are usually labeled though. If you have a liquid out port on your bulk tank all you need is a high pressure hose, a few valves, and a scale.
Look up filling paintball tanks. That's a pretty common process. It would be the same except you would have to have a different connector on the end of your filling hose.
If you do this - it is critical that you do not overfill your tank.