Quick and dirty way: For 4/4, change your time signature to 8/8 or 16/16. You can try using a delay FX on the metronome bus, but you'll get two or four emphasized downbeat clicks per measure. Or you can make a custom click track using MIDI. EDIT: Oops. Just remembered that SONAR added "Beat Subdivision" option to the metronome properties a while back. Try that.