I am interested in best technique for this also - I will be shooting from a helicopter in NewZealands south Island in 3 months time.
OK up here on the GBR Aust do quite a bit of Heli stuff-- my ways/ observations /etc.
A : Make sure they get you the BEST pilot that understands snapping from the Chopper --discuss with him what is required in Detail BEFORE you get airborne.
B: Be aware of the Rules and Regs of the Area you are working-- do NOT encourage or berate him/her if the rules are NOT to be broken--i.e 500 ft min drop /etc.
C: Observe ALL safety regs to the letter. For Shooting they will take the Door off for you-- ask for the one BEHIND the Pilot if it is 4 Seater. If only a front 2 seater- they probably will NOT take door off so you
will be stuck with the piddly sliding window--PIA's but make do.
D: Make sure to your satisfaction all Harness/ Communication/headphones /etc work --it's bloody noisy and drafty up there with the door off!
E: 500th rec SSpeed try not to lean touch any side panels-vibration/etc. Pola if required.
F: Watch for flying Lenshoods in the side draft/etc!
G: Overall be prepared- cards/lenses set exposure /tests /etc and take a deep breath and keep relaxed.
Interestingly the big Heli shooters up here in North Oz that worked on Speilbergs "The Pacific"/ Sea Patrol/ Fools Gold/ Survivor/etc all told me they charge Double for Heli snapping-- Hmmm!
Ha Josh--ah yes the South I of NZ my old stamping ground-- you will see some incredible Vista's down there-- on a good day virtually unique--good Luck.
The Heli boys down there are legendary--ex Deer recovery Pilots-- they know their craft!