Rotafix the cog onto the freewheel side, put a bottom bracket lockring (same thread direction as cog) on, tighten it. Ride around without using any backpressure. Retighten the lockring.
Use a brake for hard stops, periodically check that the cog and lockring are tight, and it should work fine for a long time. Skidding should be fine, but take it easy on the hard skip-skids.