Gain a small amount of speed (<1 tile is enough) and jump through the transition, pressing right against the door frame.

Entrance condition:

{
  "comeInWithPlatformBelow": {
    "minHeight": 10,
    "maxHeight": 10,
    "maxLeftPosition": 2,
    "minRightPosition": -2
  },
  "comesThroughToilet": "no"
}

Requires:

"canCrossRoomJumpIntoWater"
"HiJump"
"SpeedBooster"

Dev note: This strat only works for platforms that are 10 tiles below the door transition (Crocomire's Room). It could be done for a platform 9 tiles below the door transition, but this would require a momentum-conserving turn-around (or more horizontal speed); it is easier to just do a standing jump or spin jump in that case.