You might consider trying an "accel" alias modifier, so that you don't have to specify both Ctrl and Cmd. That's what Mozilla does: https://developer.mozilla.org/en/XUL_Tutorial/Keyboard_Short...

If you really do want fine-grained control, for example, so that Cmd works on OS X, but it maps to something else entirely on other platforms, you can still use Ctrl and Cmd.