Weighting in on issues like this (the
homeless guy they want to move on) you need to tap into:
Power
Authority
Influence
Different people have those three ingredients... e.g. the local Catholic Bishop may have 'influence' over the Mayor, another large service provider who is on the old guy's side is an 'authority' commentator... the minister for health has power over the Social Worker and the Mayor has power that may be used to grant the man the public property so it's now his private property and no one can trespass. All of the above have the influence over the general public to sway them in any direction, calling for his removal / protection, or for people to leave him alone.
Power, Authority and Influence... the good friend of every Social Worker or person fighting for Social Justice / Change.
Brainstorm a map of power / authority / influence on any issue and you will know where to play your cards and puppet your strings.
This is something I often sit down and draw out when I'm getting involved in a situation where a person doesn't have personal power them self and wants my assistance. It's about cultivating influential relationships, positioning yourself as an authority (or finding a sympathetic authority spokesperson) and bringing them to bear to facilitate those who have the power to use it one way or another.
Motivating the players:
All you have to do to motivate and position people with power, authority or influence is work out what they want or what their values are. Then speak to these needs / wants. The politician cares about public perception, people like the bishop care about the dignity of the person, the authority service provider cares about the person and others in a similar position (and their funding / ongoing ability to support their target group), the public care about what you tell them to care about. Businesses care about profits / public goodwill if it's tied up in profits.
Step 1: List the stakeholders
Step 2: Identify those with power, authority or influence
Step 3: Find the motivator for the players / stakeholders
Step 4: Arrange your dominoes
Step 5: Set the campaign in play
Note: anyone wants to call me a sneaky little s.o.b., that's fine

I'll fight with everything in my arsenal for my
homeless friends.