In a normal system, the freon (or rather the lube added to the freon) is the lube for the compressor. There should be a safety on the AC so it won't turn on if it's empty. You should be able to put 12v to the wire goin to the compressor clutch and force it to engage (that's how you turn on the compressor wth an OBA setup), but be careful to not fry it if your system is empty. As far as converting it to OBA, it's up to you to keep the compressor lubed. When I did it in my XJ with the factory AC compressor, I just poured oil in the compressor occasionally. A better way to do it is with an air tool oiler. You'll also want an oil separator after the compressor, as that type of compressor blows out a lot of oil into your lines. Make sure the output coming from the compressor is a high temp rated hose too.
Hope that helps. I'm waiting for the AC to die on my Jeep so I can convert it. I hate electric compressors.