This is a good one. But unfortunately it is not something I could do easily.
TotalFinder works by injecting my code into the Finder.app process. That way I'm able to modify the functionality of Finder.
You request a system-wide modification of "Open/Save" dialogs. That would require a code injection into every possible running app in the system. Because standard Open/Save dialogs are implemented in a system library which gets linked into every running GUI process. It looks like Finder but technically it is a different code.
I'm sorry. btw. This is also the reason why TotalFinder features like "Folders on Top" do not work in standard Open/Save dialogs.