Another idea might be to require that the developer first offer to rent a unit in the new building to all the old tenants, at their old rent, if they want to move back after construction is complete. A side-effect is that this doesn't encourage the developer to build something nicer than what was already there. But in some cases that might actually be a good thing.

But yeah, these sorts of things generally reduce the amount of money available to do the new development in the first place. But maybe that's ok too?