how about this?
Buy a 7kw generator and put it in the boot. bolt it to the floor of the boot and cut holes for exhaust, power out, breather for fuel tank etc.
We can't use the onboard charger because nissan have programmed it not to work when driving, therefore we have to splice into the main HV lines from the battery. https://www.youtube.com/watch?v=UcGoSO_uRXs
The generator would need to be modiffied to make 360v. this could be done by hacking the engines' governer to make it run faster.
The voltage regulator of the alternator would need to be hacked also to control the charging voltage to match the varying pack voltage during driving.
This could be done with with a potential divider over the volt sense wire to the regulator circuit. - maybe controlled by a pot accessible to the driver?
Alternatively you could use an electric furnace controller (ive charged ebike batteries with these) http://www.ebay.co.uk/itm/AC-220V-5000W ... SwbYZXdkHE
The output of the generator would be bridge rectified to make rough DC and could be feed straight into the splice in the battery connection.
the battery will smooth out all the peaks in the DC.
You would have to start the generator after you switch on the car and remember to switch off the generator before you switch off the car or You would have the same issue as leaf xpack (@4:19) https://www.youtube.com/watch?v=6Zivzvh9Bx0
. (this could be controlled electronically)
With 7kw you could drive 40mph with out discharging the battery.
A 7kw genset can be had for under a £1000 but buying a PHEV like the volt costs big money.
you could save £5k by doing this over buying a volt.
Also it would help extend the life of your battery pack if degredation was starting to affect your commute.