Cornerstone does not yet officially support Kaleidoscope 2, so to work with the latest beta of Kaleidoscope 2 (Build 99 and up) here is how to get set up:
Follow the instructions here Cornerstone External Compare Tools under the heading Custom Compare Scripts
The custom scripts contents should be
#!/usr/bin/env bash /usr/local/bin/ksdiff --partial-changeset -- "$1" "$2"
The script you create needs to be executable for Cornerstone to use it, so at your command line:
chmod +x /path/to/script
Now we don't need to wirte a script any more, just install ksdiff(http://www.kaleidoscopeapp.com/ksdiff2) works ok.