Creating a Carpet Bombing attack
All you have to do is create a weapon that is almost identical to the one asked for by Chemtrail. But instead of giving it a warhead calling for gas clouds (though that would be possible as well, but I cannot possibly think of any weapon with that characteristics), you give it a warhead for targeting purposes (wthout any animations) and, for consistency, a Damage of 1. The projectile gets Dropping, Cluster=x and Airburst=yes with a valid AirburstWeapon. Remember to put the AirburstWeapon on a Dummy unit, or you'll get IEs! Once the aircraft flies over its target, the weapon will spawn x instances of the AirburstWeapon in all directions, thus creating an effective area bombing effect.
I've worked with this method to what I think to be great results. The result can be seen here:http://forums.revora.net/index.php?showtopic=59806 (On the second picture)