There is a tutorial somewhere on how to do this. It requires a driver mesh and some graphics utilities. Sorry I can't be much more help, but I can't remember where I saw the how-to on this, otherwise I'd post a link.
You are right John. Someone did this back in 2004 / 2006 and you had an "asset" in the form of a driver with a hole where the face would go. Add your pic and give the driver a name etc and off you go. Too far back to remember who it was though.