Hi,
You probably already figured out a way to discharge, but maybe this added info might help you out.
The DJI battery will automatically cut off at 9.0 Volts whenever it is being discharged. It will not allow the battery volts to drop below that point. So you could use 12 volt bulbs or a hi wattage 5 or 10 ohm resistor to discharge the battery to that point (but try not to exceed a rate of about 2 amps). Example, a 10 ohm resistor connected to battery at 10 volts equals about 1 amp discharge rate. Deep cycling isn't really needed to be completed every flight, but DJI suggests deep discharging every 10 or so flights. I do mine by at least 15 flights and all seems well.
After you deep discharge, it would be a good idea but not required to slow charge for the first 10-15 mins. I purchased a DJI spare part battery connector so I can charge/discharge the battery outside of the Phantom. The stock chargers start out charging at about 3.5 amps and taper down to just a few milliamps at the end. This is where a programmable lipo charger/discharger would be very useful. Because if you can charge the battery at about half that rate initially will "help" prevent any damage or swelling of any cells and will IMHO prolong the battery life and flight times.
I am sure others have different ways of doing battery maintenance but I have batteries with almost a hundred cycles that are still flying strong.
Hope this helps!