This requires a 20 pixel gap between the enemy and ceiling, the same number of pixels as Samus' hitbox when in the aim down pose.
Either perform a very precise down grab to get onto the enemy or use a neutral damage boost to remain inside of the enemy then jump and aim down to land on it.
If Samus is not standing, press forward or up to stand, then jump through.
There are few examples where this is necessary, which include:
extremely tight spaces where an enemy cannot be positioned lower for an easier clip, underwater without Gravity, or in many locations while preserving a flash suit.
See also: Tech Page