It takes around 4 minutes to get the Zero to this door. Let the Zero climb the right wall and jump on top of it in Morph Ball form to bounce up to the Cacatac platform. The Zero only moves on camera and the camera scrolls when exiting the morph tunnel. Let the Zero lead through the morph tunnel or wait for the it to get very close to Samus before touching the scroll block at the exit.

One setup is to do regular jumps while aiming down until the camera stops lowering, and then let the Zero move off camera. And then crouch jump and morph directly into it, while holding right.