Good editing & for sure you could film the scene outside a bank type looking building(not to cause unwanted attention from the SWAT team) then ask the local library or fancy building owner type people can you film near the main entrance for a short while, usuall ok if they are arty places and arty places usually have nice entrances!. find a tall ceiling in the building and use a few tables ,props etc to form your 'bank' then do the robbery scene there, I can see it in my mind but find it hard to explain, d'you get what I mean?
~m