Get in the corner with the mochtroid, crouch and hold both angle up and angle down to have Samus aim straight up, and then freeze the mochtroid. You then want to do a jump and then press down immediately (do not spam so you do not morph) and it should put Samus in a standing position inside the mochtroid. Do another jump and press down and you should be in a position where you can press up then jump to clip through the floor. If you have trouble with the second down input, you can hold down the entire time and you will automatically down jump on the first frame, making it work every time.