Position below the door, jump when Samus reaches 7 Energy, and mid-air morph, timed so that reserves trigger while Samus still has upward momentum just before Samus would hit the door. If done properly, the R-mode standup will cause Samus to clip past the door shell.

With a mid-air morph, this has a 5-frame window for the jump. Otherwise, with a jump aim-down it has a 3-frame window. If Spring Ball is available, jumping in Spring Ball increases the window to 6 frames. In any case, it may help to pause abuse: instead of jumping at a precise Energy value, set reserves to manual, wait until Samus is close to zero Energy, and press pause a moment before jumping, so that Samus is at 0 energy and in position just below the door when the pause hits. Then set reserves to auto (and re-equip Varia if available), and unpause.