Hi! You have a good idea, but it's actually a bit more complicated than that. The VRAM upload in the sprites area is permanently disabled in the SGB BIOS, like the "SNES Sprites control" function. According to the SGB documentation, you can set a flag for the VRAM upload to send data to the sprites area, but in reality, the code of this function in the SGB BIOS disregard this flag and always send data to the "background area".
It may be possible to patch the SGB Bios to restore the VRAM sprites upload, or to try to manually send graphics data a few bytes at the time using the general "SEND DATA to SNES RAM" function. Thanks to Nenson Dubois research, this function is used in my game to patch the SGB Bios to enable the "SNES Sprites" function, so there is still hope that it may also be possible to restore the sprites VRAM upload too.
But regarding the sprites flickering, I fear that this issue will never be solved, as I think that's what led Nintendo to disable the "SNES sprites" function in the first place. As the SGB Bios read the Sprites OAM data from the content of the GB Screen sent by the SGB (so from a portion of SNES VRAM actually), I don't think the SNES will have the time to do everything and maintain a 60 fps update.