Does anyone have a pic of their drag brake setup, and “how to” info? I’ve heard Roger talk about using these http://www.unicycle.uk.com/shop/shopdisplayproduct.asp?catalogid=784 and wondered what was needed to implement using them.
You might want to do a search for brake, but here’s a thread about the brake I 
installed on a Coker 
that can be used as a drag brake. Complete with pictures. 
Sarah Miller and Paul Selwood have these on their cokers.
To implement it, attach one of these levers instead of the brake lever and fit a cable operated brake, I believe they have side-pull caliper brakes, which worked okay on the stock coker rim.
If you want a drag brake lever in addition to a non-drag brake, you have to do more complicated things with the cable. Sheldonbrown.com has something with a nutty double brake lever setup that might help here.
Joe