This works like a dream - thanks Mandoble! Architect, it's kind of cheating as it just creates the flares rather than having them fired, but am thinking it can be set to a team leader unit who could fire it every time the player is spotted, for example...
; flares.sqs
; creates flares at given point
_launch_unit = _this select 0
_flare_number = _this select 1
~5
#flares
_flare1 = "F_40mm_White" createVehicle [getPos _launch_unit select 0, getPos _launch_unit select 1, 150]
~20
_flare_number = _flare_number - 1
?_flare_number < 1: goto "end"
? getDammage _launch_unit > 0.9: goto "end"
goto "flares"
#end
exit