Hi Dave I just press start right before take-off and and stop after landing. I found that is the only way but someone could prove me wrong!!
For those with a 5D MK III, (and perhaps a magic lantern for 5D MK II) I have set up the camera to start recording on shutter press and then used a wireless shutter trigger to start and stop recording remotely. Without Magic Lantern for the 5D MK II, I don't think there is any options for remote start.