Hi Zach, thank you for purchasing.
Unfortunately this is technically very different problem. And TotalFinder cannot do that. Open/Save dialogs are implemented in system frameworks, they look like Finder, but they are not part of Finder. To modify their behaviour I would have to potentially inject code into every running application in the system, which sounds as a bit too much. Also some apps are sandboxed and they have different mechanism to interact with Open/Save functionality, which is another complication.
This feature has been requested many times, but I wasn’t able to implement it. I’m sorry.