Force basecamp to make a simple left turn.

In designing a route in basecamp I need to make a left turn at an intersection. Instead of making the left, basecamp takes me around three streets making right turns that eventually takes me where I want to go. This is not a divided street and there is no traffic lights. It is just a sharp left turn that basecamp just doesn't want to do. I have allowed u-turns and shortest distance but nothing changed. Any ideas how to force a simple left turn?