There should be two wires coming off of the compressor. All you need to do is tap in to one of those wires with a needle type meter probe and feed in 12 volt power from any place that is convenient. You do not have to have the engine running to tell if you have picked the right wire. You will hear the compressor clutch engage and disengage. Once you know that you can energize the compressor, then you can start the engine and try adding freon. Make sure that you are doing all of this away from any fan or belts that could grab you and ruin your whole day.
Obviously this is not the preferred method of repair but it may get you through this crisis.
There may actually be only one wire, if they are using the compressor case for ground. In that case it is easy to pick the right one.