The easiest way to set up G-mode is to lure a low Mella to the door, take a hit, then jump and aim down and freeze it while it is high enough and still rising. If the Mella is not moving upwards, there is a good chance that Samus will be in a falling state as she is hit through the transition and can't use X-Ray. If Samus does not stay on the Mella, she can spin jump or midair morph directly onto the Mella without touching the transition. It may be worthwhile to keep the other Mellas alive so that on a failed attempt, Samus can freeze the Mella to go farm some of the others in room.