I’ve just found a fan-edit of the scene, in which Kirk leaves the Enterprise through the airlock. The creator (pun-intended) made his own matte-painting of the Enterprise’s saucer section around the airlock-set.
This really looks awesome and I’d love to see it in some form in future fan-edits of TMP.
However, I think for any purist rebuild of the Special Longer Version like FanFiltration’s, I think it should stay in it’s original form with the soundstage intact.