Well I would do like you said
Have a Pokemon that has a modest nature with the synchronize ability Abra Faimily, Ralts Family, Mew, Umbreon, Espeon, Natu Family start off with that Pokemon and then switch out to another pokemanz then catch it the synchronize ability increases the chances encountering Pokemon with the same nature as it and if you wanna breed natures give the mother an everstone and you'll get one with the same nature as the mother Pokemon