Bronxbull is right. freewheels, brakes and velodromes don't mix. Imagine coming around the pack three wide doing 65 kmh in the last 200m on a big, flat Aussie track and have someone sit up and start freewheeling in front of you!!! Be sure to have the brown skinsuit on.
Didn't the Canandian Joc Lovell ride the kilo at the Worlds in the early 80's with a dual drive bike? If I remember it had chainrings on both sides, and a cog on each side of the hub. He started in a smaller gear, the other cog wound on while he was speeding up, then took over when the cog had taken up all the thread on the rear hub. The small gear was a freewheel which then clutched for the remainder of the race. Jens Glulitch or Maic Malchow then probably won the kilo by 3 seconds instead of 3.000001 seconds.