To balance the light, I did two things. First, I used no red filter or polarizer, which can both add contrast in cases like this. (I could have used other filters to help reduce contrast, but I didn't want their undesirable side effects.) Second, I used my on-camera fill-flash to light the foregound. It's still a long exposure, but the flash is only an instant, and is just enough to bring up the shadows closer to the highlights created by the bright light from down below. How did I know how much flash to use? I didn't. However, the camera can figure it out if I tell it the brightness I need to match by metering on the bright area itself. This tells the camera that it needs to power the flash enough to light everything in the foreground. The background building is lit by ambient light alone as a consequence of having a longer exposure. Note: experimentation is necessary, but that doesn't take much more effort than just taking several pictures at different exposure times and seeing which one comes out best.