Brian,
I do not believe you are going to do exactly what you are looking for since there is no way to write to the control lines programatically or from the camera file. If you are looking to use this signal to trigger each line, you may want to take a look at this example:
http://zone.ni.com/devzone/explprog.nsf/6c163603265406328625682a006ed37d/f2799dc12a94be2586256a79006985ce?OpenDocument
It uses motion and routes the encoder signal across for the line trigger. You can modify this so the input trigger is from your trigger line. I hope this information helps.
Chris D
NI Applications Engineer