I am not sure where you live but any competent mechanic who has a basic understanding of zeros could install the diginow super charger for you. There is good documentation on how to do the install and it simply drops in place, is secured down, and plugs are interfaced with the bike.
The JPlug which comes with the unit is long enough you could have it installed at the default location, or if you wanted on top the tank like the "tank charger" unit is stock by zero.
The smallest unit is 3.3kW ... but you can easily fit 2 under the tank and use one Jplug.
For "power source" the diginow unit is powered via JPlug. If you have other plugs you can purchase adapters which convert 14-50, 14-30, 5-20, to JPlug on diginows site. The unit charges the bike through the AUX port, but it is also set up so you can power the stock chargers at the same time.
There is a diginow super charger thread on the forums worth checking out.
Here is the diginow website
http://diginow.it/super-charger-for-zero-motorcycle.phpYou can order them through Hollywood electrics, so feel free to call them and ask for the unit you would like to order or ask them questions. If you live near Hollywood electrics then they could install it for you no problem. You could theoretically use it as an "external" charger but ideally you would install it under the tank.
Note, this is made to be used with a power tank or charger tank ... if you have the tank with a pouch in it then it would need to be modified or replaced with one of the other units. The replacement tanks are about $100 if I recall. Again, talk to hollywood electrics