Write this in "On Activation" of a trigger:
flare1 = "flare" camcreate [ X , Y , Z ]
You've to copy the coordinates from your mission.sqm (think should be the ones from the trigger)...but notice in .sqm they're written [ X , Z , Y ] so you've to change the last two coordinates in the trigger.
Z is the height and you can change it how you need it.
Greetz
Plage