Got it! I'm not sure if this was known to be possible or not yet, but everything I've read says it's not, so I figured I'd make a post. It requires x-ray climbing out of the springball room, walljumping all the way to the top of the empty space above it, and crystal flashing through the floor of another instance of the room. This doesn't require use of the GT code or any other items that would be absent in a normal NBMB run.
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