once the shaft is broken it is really hard to fix.
but you can try this-
find a dowl rod that is as big as the inside of your shaft.
cut both pieces of your shaft so the break is even- that is so there isn't any carbon splinters or crap sticking out-
cut about a 10 inch + or - piece of the dowl rod and try to insert it into both pieces of the broken shaft- epoxy it in place and hope for the best.
i would definately only use it in emergency situations