The last time I took my 450 as it is, just made sure there were enough soft things all around it.  Also, I made sure the the area outside/surrounding the heli was packed taller/higher than the area of the heli itself, so that any pressure from bags placed on top were handled by the areas that are higher than the heli.

For larger helis, just remove the boom, skids and either the main-blades (or the whole head).  I have also noticed that if you ask the airline folks to put a "Fragile" sticker on any particular bag during check-in, the airlines/airports do seem to take some extra care about those.  I was able to transport ARF balsa planes this way, with out damage.  If anything were placed on these boxes, I would have ended up with lots of spare balsa