I remember talking to a fella who made one for a drill press awhile back. If I remember right it was nothing more than a fence with a dial indicator mounted on it. Getting the readings from the shaft of the sander mounted in the drill. YOu know how thick the piece is, simple subtraction will tell you how far you need to go. You could make a 2 fence system with some all thread on one end. Using a knob on one side and have it threaded beneath the surface of your actual lam fence. It would allow you do some pretty fine adjustments.
of course its a hand fed deal.
To get tapered lams, you can buy templates from old master crafters.
It aint perfect but I bet it'll work good enough for ya!