Tape the broken section with any kind of plaster,One that you would put on a cut then stake the plant well the arm on the plant that has broke support with the stake and tie it to the stake it then will be fine.You will be supprised how hardy cannabis is i have had plants snap and found the exact break put it back togeather like a jig saw and after a few week the plant has grown a secondry membrain over the break.Tape it up even at 6 week the last two week are normaly the most productive for crystal production what you got to lose.