The only experience I have with this is probably not worth sharing because it did not stop the crack. Any bit made to cut metal will do, just be sure to use some type of lubricant to dissipate heat and don't try to go too fast. I would suggest about a 3/16" to 1/4" bit and drill about 3/16" past the crack. Cut a little and back out to let the cymbal cool a few seconds and repeat.
I used a 1/8" bit, if memory serves me, and drilled just past what I thought was the end of the crack. Within 3 or 4 months, it was cracked past the hole. I think the crack probably went further than I could see, and I should have used a larger bit.
I haven't let anyone sit in on my kit since the night this cymbal initially cracked. You never know how hard the next guy plays...and this guy beat my kit like it had done something bad to his mother! Of all the cymbals I have owned, that's the only crack I've ever experienced. OK, I'm done with the Soap Box.
I wish you luck! Maybe someone that has had success with this will chime in.