Though it is a different kind of battery; we have been charging 6-24 volt automotive batteries while in use for over a century. It certainly CAN be done on the leaf as well. The problem to overcome is the limitations of the built in level 1 and level 2 charging ports.
At Level1 120 volts 15 amps:
It takes 18-24 hours to recharge to a 90 mile driving range. In other words if one charged at level 1 charging voltage and amperage, it would add a whopping 6 or so additional miles of range to dead battery.
At level2 240 volts 30 amps:
It takes 4-6 hours to recharge the battery and it would add approximately 25 miles of range to dead battery.
At level3 (Unspecified Amperage and Voltage, likely 350+ Volts at 100-150 amps:
It takes 45 minutes to recharge to 80% driving range. This as well as a slightly slower charging rate could keep the battery charged while driving though it would mean working with extremely dangerous voltages and amperages while risking battery over heating, explosion, and useful life.
I am not saying any of the standard level 1-3 charging ports can or should be used for charging while driving; if they could be rigged with overrides and software programming changes made; it would certainly void the vehicle's warranty.
The question is a very valid question that any thinking, intelligent question would ask; If 80-90% of the vehicle's use will be under the normal driving range, why would a sane person want to carry the weight and loss of cargo space to a generator of battery extender pack that will rarely if ever be used?
A trailered range extending generator, could not only be used for the occasional long journey or ferry of the vehicles; but also serve double duty as home based back up electricity generation. it is an intelligent choice for intelligent people, the cranial impaired should rent a car, or better yet, take the bus.
Gizmag has sponsored several EV extender schemes:
http://www.wired.com/2010/11/range-exte ... your-gear/
http://www.gizmag.com/rinspeed-dockgo-c ... 3/pictures
http://www.gizmag.com/ev-charging-trail ... 3/pictures
There are others.
My feeling that the best scheme would be to transform and rectify filtered DC voltage and amperage directly to the battery during the long range commute and allow the normal recharging battery maintenance system maintain equal charging to the cells during recharging cycles. It would also be best to deplete the battery for recharging towards the end of long range trips in order to allow the vehicle BMS to properly equalize and maintain the battery during a full cycle recharge.