(resisting temptation to say "put helopad down")
I know there is the command:
heli land ""LAND"
....which lands the heli when you activate it in, say, a trigger. Other possibilities for your problem are that the heli is moving too fast and overshoots a bit, sometimes causing him to land a distance away. Try solving this by placing a few WPs before the landing point, which slows it down and/or changing the speed mode. Also, make sure that the landing area is reasonably flat and has a reasonably clear airspace (not too close to buildings, trees, etc). The AI can be quite observant about this and refuse to land if the ground is too steep, etc.
Otherwise just use an invisible H. Ooops. Sorry!