I don't think I'd even worry about it - as Ray noted the end of the leaf may just die. When it does, just cut at the crack, by that time the exposed part will have dried and sealed itself. Treat the puncture, let the rest just do what they will. Once the broken end dies, you can cut along the break with a single-edge razor blade... it makes a clean cut, and you can use a new one for each plant so that you don't have to worry about sterilizing tools.