I want to do something more with Hellenism, but thus far I haven't been able to come up with ideas that make it sufficiently different from other faiths. Also, I'm maybe hoping we get a flavor pack that focuses on the Byzantine/Greek region that gives me more to work with.

perhaps instead of patrons you could tap into the mystery cult and philosophic traditions around helleno-latin religions. and the deification of individuals after death.

you could have membership in secret societies that follow various figures or adopt a philosophical tradition like neoplatonism. sort of like how there's different schools of islam in eu4

That would be a very big investment, using mechanics the game doesn't even currently have (so I'd need to code them myself). That goes more than a bit beyond what I've done so far, so I don't think it's likely to happen anytime soon, as neat as an idea as it is.