I think, in this situation, I would have tried to arrange for the sick person to be taken home, either in a cab or by a co-worker and would then have blocked in the offending vehicle, leaving a polite note on the windscreen telling them where to come to get the block (another car) removed. When they turned up there would be a lecture on the unsocial behaviour they demonstrated and they would be told that they would have to kick their heels for the next two hours as I was too busy right then to leave the office (due to having to take time out to take my sick colleague home). With any luck they wouldn't park in my car park again!