I don't think Thornley and Hill were really harkening back to the other enlightenment religions, that's not to say that they don't share a lot in common, but there's a kind of repeating motif in philosophy religion.
More likely, if they were deriving from anything, it was existentialism.
Thornley also poked fun at es background in Mormonism, but I think a bit of real Mormon philosophy crept in (the idea of creating/becoming your own god/dess and proclaiming yourself pope/saint, for example).
(To be fair, this post comes from a discussion about this topic I had with my friend Alden)
The Discordian philosophy of there being objective Reality, which we interpret through our personal-cultural grid as our subjective reality, quite possibly comes from Existentialism's idea that the universe exists outside of personal perspective, and that each individual can chose es own morality that works within that concrete universe.
We believe that existentialism owes a lot to the Biblical book of Ecclesiastes. Please forgive this oversimplification in ignoring differing points of view and reducing complex philosophical systems into nutshells:
Existentialism: Our lives have no ultimate purpose; everything is meaningless; life is a bore; everything is absurd. You may choose to eat, drink and be merry, for tomorrow we die; we end in nothingness. There is no God.
Ecclesiastes: Our lives have no ultimate purpose; everything is meaningless; life is a bore; everything is absurd. Eat, drink and be merry, for tomorrow we die; we may well end in nothingness. There is a God.
It's probably for this reason that Christians seldom quote Ecclesiastes, except for the "there's a time for every season" part (which I like). I find it fascinating that a book of the Christian Bible contradicts much of modern day Christianity. Principia Discordia
uses parts of the Bible and Christian theology/methodology to contradict it too.