I would guess there is about a pint of fuel forward of the fuel selector so once this is turned off there is very little to support combustion forward of the firewall unless you have had a major engine failure and then you have eight quarts of oil inside the engine to burn.
My advice would be to do the fire drill in the flight manual and fly a standard Cessna 172 forced landing just like you practiced in your trainning, the fire will have almost certainly burnt its self out by the time you get on the ground.
IMO the major risk from am an engine fire is getting the forced landing wrong and if you try any of the Spitfire techniques mentioned above the forced landing will take the average PPL into unknown territory and is likely to result in mishandling of the landing.