poor mans digitizing gizmo

hi all

i´m trying to figure out how to create a dxf contour from a porclain
bathroom countertop. in fact, i cut and mill out a lot holes for
porclain and corian sinks in countertops, theres never 2 identical
ones. today i have to measure, calculate, use radius templates etc.
to get enough info for making a cad file. i saw one of these
digitizing arms (costs a fortune)with a probe in the end that one
just draws along the periphery and voila´ in a sec the dxf pops up.
would it be posible to build a simple lo-resolution digitizing table
with scrapped mouse parts, encoders etc.? i was thinking of arrange a
mouse on a sort of pantograph arm or gantry.
has anyone tried this or any similar? is there even any software for
this?

hope its not to OT...

js