This worked, thank you! Now the only thing left is, how do I make it so when I first open the tiddler it shows the “this tiddler contains binary data” banner in view mode? This is how other office files work. With Project files, I see that in edit mode, but in view mode it shows the gibberish text.
The practical result is that I have an extra click or two to open the Project file, versus other Office files.