In some languages, certain particles can be pretty adposition-like, yet stand by subject-like nouns:
no-one but he/him knew ...*
One could easily imagine that a language for this particular type of particle had an ergative-like pattern going on, thus
no-one but him slept
no-one but he saw it
they saw no-one but him
* This is apparently a construction where English grammars differ on recommendation, yet some standardized tests require one to take a stance, thus forcing the pupil to know which fucking grammar the author of the test holds to be correct. If you make standardized tests, you should fucking well be knowledgeable enough not to do that shit to people.