There isn't any BIS made black hawk wrecks, unfortunately. And the setDamaged version of a wrecked blackhawk doesn't look too good. But I have two suggestions:
1) SetFuel the chopper to 0 an Setdamage it to 0.5 or 0.75. Then the windows will be cracked, but the wreck will not crumble before the eyes of the players at missionstart.
2) Stick to your original idea, but place the playable units turned away from the helicopter so that none of them has the chopper wreck in their field of view when the mission starts. Hopefully this will give the computer enough time to turn it into a wreck before they turn around. Also, you can blackout the screen a few seconds when the mission starts. This will give the computer even more time to crumble your blackhawk to dust before anyone can see it. Or use disableUserInput for 2-3 seconds in the beginning of the mission, thus restricting the pshysical ability to turn around too early, or... variations are almost endless.