Simple: 'Camcreate' a grenade/smokeshell near that chopper.
_Yourbomb = "grenade" CamCreate [GetPos _MyChopper select 0, GetPos _MyChopper select 1,-1]
I use '[GetPos _MyChopper select 0, GetPos _MyChopper select 1,-1]' instead of just 'GetPos' chopper to avoid the grenade of exploding in the air an damage your heli.