Well Quasi Deities can recieve or hear prayers, so I'm not sure how that would work, but since it only has to be granted once I suppose you go visit the Quasi Deity in person, but this has weird implications.
Here is the list of Titans creatures in 5e
1. Empyreans, kid of a God or 2, so I can see that making sense.
2. Kraken, weirder, but Kraken cults are not unheard of and they do create a kind of divine spellcaster so it could work
3. Atropal aborted God or something, weirder still, but it still makes sense
4. Tarrasque, mentioned in the past as having some worshippers
5. This one is the really weirdest one, Astral Dreadnaught, I find the idea of worshiping one till it ascends to God hood funny and the idea of someone some how becoming a Cleric of a random Astral Dreadnaught funnier.