Dahon Curve Winter Wheels:Removing Novatec F316SBT single speed cog without lock ring

Hi folks.

Given 8 weeks of snow last winter in Vancouver and the prediction of more this year thanks to la nina, I'm building a set of winter wheels with studded knobbies for my Dahon Curve. I bought a set of wheels with a single speed hub and want to replace the 9 tooth cog to gear the bike...