Re-circulating heater

[john.p.clegg]

Nothing much to do while it's cold and damp (apart from re-building the gearbox,re-camming etc.,etc.) and the thought comes back to the woefully inadequate heater on the Plus2, now I know it's partially my fault because I can't be bothered changing the summer thermostat for a winter one but I still have the idea in my head for fitting a re-circulating flap in the cold air intake.....has anyone done it? (Apart from all the major manufacturers...) I do have a spare pull/push control (the old choke)...

Any ideas?