Hmm. I've seen this "bomb shooting" before: it was on a public server when some cheater removed our base with his assault rifle.
Whatever.
This could be done from a units
Fired event handler:
* spawn a bomb where the projectile is (createVehicle, getPos)
* point the bomb where the projectile points to (vectorDir, vectorUp, setVectorDirAndUp)
* set the speed of the bomb (setVelocity)
* delete the projectile (deleteVehicle)
Note that you'll lose the original ballistics this way.
Edit: