Minderwiz
In his surprisingly lucid astrological treatise, "The General Principles of Astrology," Aleister Crowley weighed in against throwing over the traditional rulerships but wanted a way to integrate the outer planets into the scheme without upsetting the symmetry. He proposed the concept of "superior governors" in the sense that they operate on some kind of a "higher octave" principle. Other than the usual suspects (Uranus for Aquarius, Neptune for Pisces and Pluto for Scorpio) I'm not entirely clear on his basis for "what goes where," but I know each sign had such a "governor." Although he seems to have decried the Theosophists, this certainly smacks of their spiritual imprint. I don't have much patience with "spiritual astrology" (I never could get through Alice Bailey) but if I can run down his basis I'll give it the "giggle test" (i.e. if it doesn't make me giggle I'll perhaps think there's a chance - however remote - that he might be onto something).
I wasn't thinking of anything to do with signs. Something more along the lines of Neptune ruling scrying glasses or vague ideas, or Pluto ruling huge lottery wins (it needs to be associated with some good things).
As with all such rulerships there's bound to be disagreement but it allows the outers to be 'rulers' in some sense or other. The trouble with the idea is that whilst Uranus and Neptune are bona fide planets, Pluto is a dwarf, and if we allow one dwarf we have to allow the other six (well actually there are only five other dwarfs at the moment but I'm sure another will be added soon). Then there's asteroids and other bodies, so perhaps my idea was a bad one to start with (though that in iteself may justify my Neptune affinity rulership of vague ideas)