What about grafting autoflower plants onto a photoperiod mother??
EDIT: I guess it wouldn't be perpetual then.
SPOILER ALERT. Well sort of. I've been having such great success with grafting, that the other thought I've been having is... what if instead of pushing new branches out of the box... i just cut the finished cola of the plant and graft a new cut on... keep the lights on 12/12 and just replace all the flowers with new grafts. This is an experiment I'm also going to try for sure. After we see about the light barrier one of course. If the mass grafting technique works to turn a ready to harvest plant into a ready to flower plant, that is most likely the technique I'll stick with. Then I'll only have 3 plants. One great big MOMF and two great big plants that I just keep grafting new branches on to flower.