I've never tried this before but from what I've read you'll need something like this: Hawk-Woods PC-12 Cable, D-Tap (P-tap) to Blackmagic Cinema Camera
I use a remote follow focus which I power out of one of the D-taps... if I power the BMCC, the FF motor hardly turns... to much draw from both camera and FF.
I would suggest that you power the BMCC via a third party Battery solution..
I'm getting the indiPRO Tools Power Grid for Blackmagic Production Camera 4K (2x Sony L-Series) http://www.bhphotovideo.com/c/pr ... for_blackmagic.html (and yes it will work with the 2.5K Cinema Camera).
Since you can find after market (Third Party) Sony L-Series cheap and they simply work.
Using something like the Redrock microSpud http://store.redrockmicro.com/Ca ... amps/microSpud.html
you can mount the indiPRO Tools Power Grid to the "Top Handle/Crossbar" ( With one of the two mounts supplied by DJI ) on the gimble.
With the Internal battery of the BMCC fully charged (Gives you about 45-55min of shoot time) and 2 Sony L-Series batteries you would easly be able shoot 6-8hrs straight.