Hi -
This happened on my Octatrack. I was able to thread a long self tapping screw into it and pull it out most of the way, while gently prying the metal contacts out of the way. It was tricky but I was able to get it out.
I cut a piece of rubber cable insulation off a old firewire cable and put it over the screw to prevent the threads from damaging the inside of the jack. Once I got it halfway out I was able to wiggle it out the rest of the way with a small flat precision screwdriver.
Of course the only reason this worked is because the part of the plug that was stuck inside was hollow and I was able to grab it from the inside. Depending on how much of the plug is broken off in there you may have different results and may have to use other techniques.