The SNES address $05:B29B (64 bytes) holds "the 8x8 tilemap data for the sprites used on the switch palace messages (dotted and '!' block). The first byte in each in the tile, the second byte is the YXPPCCCT data."
So one easy way would be to replace every second byte of these 64 to "F8" as this is a transparent tile. The game will then still drwa tiles there, but invisible ones.
1 
