I have seen some threads over in the DIY forum where people have hooked the hanging system to a rolling track (similar to a sliding cloest door) mounted on the ceiling, so you could essentially slide the whole light fixture forward or backward.
Did a quick Google search and it would be using something like this:
http://johnsonhardware.com/sdindex.htm
or even something like this, that seems to be a complete kit:
http://www.thehardwarehut.com/catalo...p?p_ref=237669