However, I found a method to force it to happen in English Crystal v1.0 using Game Genie codes:
Front sprite of Unown modifier:
Back sprite of Unown modifier:
Here is an example:
Unown 0x1F front and back, the back sprite plays glitch music ('Unown 0x1F true cry') wouldn't load however.
0x1B's back sprite loaded here, but the front sprite freezes so I encountered Unown A instead.
Edit: It also works on summary screens. ^^ Time to go through them all again. Will port the codes to EN Gold/Silver soon unless someone beats me to it.