Create a Nautilus extension using the Nautilus Python bindings which acts as a NautilusInfoProvider to hack the NautilusFileInfo object for directories. If the directory contains an AppRun file, then change its mimetype so that it's application/x-appdir. That mimetype should be handled by another program which sets the right directory and runs the AppRun inside.
Problems:
- You don't seem to be able to override the icon for a file. (You can add emblems.)
- This is an evil hack.
There is apparently a way to do this without the extension:
12:20 < gicmo> if you choose properties on a direcotry you can specify
different programs to open that dir with ..
12:20 < quinn> gicmo, I don't think that works with the new MIME-type system
12:20 < quinn> At least not in spatial mode
12:21 < gicmo> quinn, ahh right .. haha .. you can add programms but I wont
work ..
12:21 < gicmo> thats kinda non-intuitive ...