Stand facing away from the door in the previous room, at a specific distance from the door, approximately a 2-pixel window at an effective distance of 3.7 tiles (taking into account how slopes can modify the effective distance). Pause, then unpause while holding dash and right. If positioned correctly, the unpause fade-in will finish on the exact frame that the transition would occur, delaying the transition by a frame. Samus will spawn standing inside the Power Bomb blocks and be able to X-Ray climb.