Cool idea! In theory, you could put a force sensor under each corner of a piece of glass and calculate the touch location by analysing the four sensor readings. The calculation would be like finding the center of gravity. These calculations may not be exactly right, but I think they are a good starting point.
x position = W*(combined readings of 2 sensors on right / combined readings of 2 sensors on left)
y position = H*(combined readings of 2 sensors at bottom/ combined readings of 2 sensors at top)
where W is the width(x direction) of the glass and H is the height(y direction) of the glass.
The only way to find out if it works is to try it! It sounds like a fun project - I would be trying it right now if I had the sensors.