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Hi Chris - try this, heat your lens hood but not the lens. Put the hood very close to threading in with maybe a 3 or 4mm gap. Cover this section with sticky tape or cling wrap so no air can pass through the gap. Point the camera up at the night sky with the heater on. My theory is you will have dewing as fast as you would have if the heater weren't on at all. My thinking is there will be no heat transfer from the hood to the lens body. If you are right the warm air will keep the lens from dewing. The heat should be as much you would normally use. You could heat the lens with IR from the hood if you had it hot enough.
I don't have a dew strip to try it so you will have to be the myth buster if this thread is ever going to be resolved (in my favour).
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