Matt,
You can actually do an Auto Ingest from a card reader by using the Live Ingest mode. Just set the path to your card reader then pop in a card. Live Ingest will search the card but will not unmount the card from the desktop, the way Auto Ingest will. The card reader should tell you when the upload is finished when the blinking activity light becomes solid. I don't know about Windows but a Mac will give you an alert when a card is pulled before it has not been properly unmounted. That alert will go away after about 30 seconds... there's a good chance you won't even see it.
Essentially, instead of tethering a camera to PM, you are tethering a card reader. It works.