Fixed Gear Bike

[RSD]

I have an unusual question I'm hoping to get answered on this forum. I've got a fixed gear bike that I want to convert to a horse training device. How do I get the rear wheel to become free wheeling, so I can turn it backwards as well as forwards? It has a bendix brake on it. Do I need to remove that, and if so, is there a special way to tighten the chain and hub? I'm kind of grasping here, so hoping someone with bicycle knowledge can help me.