An easy way is once Samus is on the top platform, jump and aim down to lower the camera, then place 3 PBs.

Requires:

{"enemyKill": {
  "enemies": [["Metroid", "Metroid"]],
  "explicitWeapons": ["PowerBomb"]
}},
{"or": [
  "canMetroidAvoid",
  "canCameraManip"
]}

Sets flags: f_KilledMetroidRoom2