Today at our local hackerspace I did some calibration of the stretch sensor prototype I had finished. I was assisted by some other people who hang around here, who helped me out a bit with ideas on how to adapt the code in the best possible way.
I adapted the teensy code through adding some mathematics, and used a different resistor to get the values I wanted. By using another resistor I could also work out the issue of how much power the Teensy can output, and thus I can add more stretch sensors without having to add an external power source!
These modifications and calibrations allowed for the sensor to properly output into a MIDI OSC-control! I quickly noticed the signals from the stretch sensors I had made were not incredibly stable, but I figured that the alterations were so small it wouldn't have any real implications in most practical situations.