Not sure how useful this would be in practice in actually warming the battery. Have you measured the battery temperature using Canion to check that it does much ?
The Peugeot Ion doesn't support pre-heating mode like your i-Miev's do so in the winter when the windows are either iced or likely to fog my routine is this:
An hour before going to work, I unplug the car from the charger, turn the car on using the spare key, set the heater on full blast on the windscreen as well as turning on the rear demist. I lock the car with the other key and leave it for 10-15 minutes. The heater draws about 5kW for the first 5 minutes and about 3kW for the remaining time. Total energy used from the battery about 1kWh.
I then come back, turn the car off, plug it back in to a Level 2 charger (240v 3.3kW) for about 45 minutes to reach full charge again.
I've checked the battery temperature rise on Canion a couple of times and it was only on the order of 2 degrees C at the most - so barely worth it from the perspective of warming the battery.
However, not only does it de-ice the car and at least take the chill off the car (it cools down in 45 minutes, but not back to its initial freezing condition) it also "pre-heats" the PTC water heater for the car, meaning that the heater is warm almost immediately when I set off.
The water heater has a huge thermal mass so it takes it a good 5-10 minutes to fully heat the water from say freezing -4C to 55C, but left to sit for 45 minutes it only drops to about 40C, so is putting out air that is fairly warm and sufficient for defogging immediately and hot within a minute or two.