AC compressor lubrication?

I'm attempting to convert from R-12 to R-134a: a source on the internet and a local repair shop have both said that the mineral oil in R-12 systems is incompatible with the newer oil, and when mixed, they will both turn to "mush". So I'm apparently supposed to drain the mineral oil from my compressor, but the procedure to charge the system involves operating the AC compressor on for 5 minutes to stabilize system pressure before turning the AC to high to add R-134a. If I'm running the compressor for 5 minutes without oil, that seems like a bad idea. Should the compressor be lubricated prior to vacuuming and charging the lines? Will 5 minutes not hurt the compressor? What lubricant would be used to fill the compressor prior to vacuuming and charging the system? Any other tips?