This is a little technique I was kicking about for awhile, and I've had varying degrees of success with it although I haven't taken the time to refine the technique as I should.
Essentially, the mage sets up his working space as he would for a necromantic working (cf). It is absolutely essential that this operation take place when the victim is asleep, preferably two to three hours after sleep has begun.
The process is simply conjuring the victim's spirit as one would for a dead person, but the mage must have a container handy to constrain the victim's spirit. This can be either a specially prepared cage or crystal, or a Prinn Bottle™.
Such a cage or crystal could be prepared by cleansing an ordinary crystal and casting a circle of protection around it (or a mirror ward if you're into that sort of thing) with the barrier facing inward instead of outward.