You probably have to turn it back to off/lock to take the key (remains of the key) out. The only way that I can think of is to put a dab of superglue on the end that came out. Then put it in, wait a while for it to stick to the broken end and then pull it out. It might get stuck in there but you have nothing to lose at this point.
How to change.
http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=genmods&Number=1034190&fpart=1&PHPSESSID= 
