early energy tanks: tower
From the top of the room, space jump off the ledge to land inside the tunnel and right below the energy tank. Turn until the energy tank would be in front of you and morph. With this camera angle, you should always get an instant morph.
Do a 2bsj or sb-bsj, and as long as you don't wait until the peak to hit C, you should always get an instant unmorph. Pull back as you ascend in human form, then move forward as you use the second jump, morphing a bit before the peak so you don't hit your head. Continue moving forward during the instant morph and you'll get into the last part of the tunnel if all goes well, but it's far from easy.