I ran into this problem recently. If you're willing to tt, go about 15 to 30 days into the future. If there's someone you want to leave with a thought bubble over their head, ask 'em. If it's someone you dont want to leave, tt back to the present, them go forward the same amount of days, and someone else might have it. Also, if you want the villager who has moved in most recently to leave, no dice. They won't. Be prepared to clean up after all the time travelling, it can mess with everything. I've only ever done it once, when I was desperate to get a certain villager.