Seems like their isn't a stick which has any effect, or which we are willing to wield. The carrot is likely the only effective method here. That will cost the cities money, but it's the only effective method.
I remember several years ago they started employing spikes and other barriers like that, in areas they didn't want them sleeping. I don't think that was effective, cost effective, or pretty. The only immediate thing they can do is force them to relocate with police officers, tasers, tear gas, etc. But that is a constant battle. They need a carrot at the place where they relocate.