Dale-of-Cedars wrote: “Yes! I essentially learned this in the last 2 days, as we had 2 different play opening nights to attend back-to-back, both with spring-loaded seats.
“Butt-lower-and-slide-back.”

Spring-loaded seats or not, and going purely on the experience of having been kilted on and off lately, I would say put the knees apart (not all that easy in a theatre seat, granted) and let the sporran do its work while smoothing the pleats behind.
Regards,
Mike