Yeah, admittedly this is one of the only areas where Conclave truly falls flat on its face and can genuinely be a pain in the rear to deal with. I feel like we honestly need more ways to influence people other than basically bribing or going quid pro quo on a vote. Off the top of my head, you'd think maybe some of the stuff from WoL could have integrated with Conclave. Use the Intriuge focus to blackmail someone into a favor, the Seduction focus to seduce someone into a favor, and maybe even the Carousing focus to get someone drunk and then convincing them to sign off on a law without them necessarily remembering the next day.
Edit: Don't mean to de-rail this thread, but I got little bit bored of studying and these just sort of popped into my mind. None of these should probably be regular events, but if these or events like them popped up every now and then it would be nice to have an extra favor here and there.
-Hunting: Saved someone's life from a [regionally appropriate animal] attack while out during a grand/tiger hunt. Character is grateful and owes you a favor.
-War: You've won a duel and decided to spare someone's life. If they are not Proud, they will be begrudgingly grateful and owe you a favor.
-Theology: Helped someone out with a manner of faith (nothing specific comes to mind at the moment).
-Scholarship: You were able to research a problem / invented something in order to help another character using your learning stat.
-Family: You fell in love with your spouse and they'll do anything to help you stay on your throne or alternatively, you're on such good terms with your family members you can ask for a favor.
-Business: You either helped a character make money (perhaps on a trading expedition?) or you talked someone out of a bad investment (carpenter's guild or the "discount castle" event?).
-Rulership: Your subjects have come to recognize that you've been trying your hardest to do what's best for the realm (you're stressed/depressed). Allows you to ask for a favor from a vassal with decent opinion.
-Lifestyle, Impaler: For an Impaler specifcally, you tortured someone in your dungeon. They wanted you to stop, so they've agreed that they will owe you a favor in exchange for their life (high chance if the character you tortured is Craven).
-Lifestyle, Occultist: For an Occultist specifically, perhaps you communed with the spirits for someone (long lost loved one maybe?).
-Lifestyle, Poet: One of your poems saved someone's love life (this is admittedly sort of a goofy one).
-Lifestyle, Strategist: You showed someone some new tactics that ended up aiding them greatly on the battlefield.