Not a template but on a slight tangeant....
I've got a theory for you guys to shoot holes in:
Using a square, draw a right angle on a rather large sheet of paper.
The horizontal should be at the top of the sheet and the vertical 5 or 6 inches in from the edge.
Now using the horizontal line as the nut location, mark the vertical line for fret locations based on any scale length you choose. A StewMac tmplate would be very handy for this step. At the bottom of the horizontal line make a mark for that scale length.
On the horizontal line at the top of the page, make a mark as far away as you can-4 feet should be a good distance for this I would think.
Now draw a line from each mark you made on the vertical line to that point on the horizontal line. Extend those lines through the other side of your horizontal some few inches as well.
Now again using a square, you can measure between the top horizontal line (nut) and the bottom line (bridge-scale length) and sliding left or right of the vertical you made, and mark out any new scale length you want. Still using your square draw another vertical line from that point. Every point it crosses the lines you made (from your original fret locations and the vanishing point) will mark the locations for your frets on this new scale length.
Of course, an accurate angle and precise markings and lines are required for the most accurate locations, but If what I remember about geometry and drafting is true this should work.
I'm sorry I don't have the resources to illustrate an example at hand.
Now can anywone find errors in this theory?
SR