I'm not sure if it will work, but Syndicate have cards that share factions with each other faction.
Skelllige: Sukrus, Hammon, Tidecloak Hideaway
Monsters: Pugo Boom-Breaker, Tatterwing, Kikimore Warrior
Northern Realms: Prophet Lebioda, Nathaniel Pastodi, Temple Guard
Scoia'Tael: Novigradian Justice, Harald Gord, Cleaver's Muscle
Nilfgaard: Doadrick Leumaerts, Rico Meiersdorf, Courier
But as I said, I don't know if it will work or if the game will consider those cards only as "syndicate" cards.