The only way to do good perspective is approaching it head on, no two ways about it. But on a digital medium, as mentioned, you can use approximate references, use tools to make a perspective grid, pen tool to make sure everything is consistent, etc etc. Those aren't cheating, they're completely valid tools and can speed up the process!
You can also use Blender for some simple 3D models to get an angle that might be hard to find in pictures. It's a little difficult to get the hang of the software, but then even putting some simple polygons together to pretend it's buildings and set the camera to your preferred angle will help out tons in the sketching phase.