Someone tried that and it will only work with officially signed-by-Nintendo demos. There's a homebrew software for Wii that takes over My Pokemon Ranch and other software to send out custom DS files, but they tried using it and the only things they could replace it with were official demos.
That thread is here if you want it: Wiireless Multiboot
As for HANS and similar homebrew software, I don't know. But I doubt it.