A more reasonable approach would be to replace your water heater with a smaller capacity unit so that you are not heating so much water. Add a timer so that the heater is only heating water when are awake and you might eliminate 100 hours of heater run time in a month.
Depending on where your water heater is located, the heat loss (other than in summer time) may not be as much of an issue as you think. If it's in a part of the house that you heat anyway, then the heat loss from the water heater is offsetting runtime from your furnace. Granted it may not be a 1:1 factor, but it also might not be large enough to be a major factor.
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