[FEATURE REQUEST] Option to Flag Mode7 Pixels Using the Alpha Channel

[ChthonVII]

Basically the title. I'd like to have an option that, when enabled, would use the alpha channel to flag pixels as mode7 or non-mode7. The use case for this would be to enable shaders that use pixel-art scaling algorithms only on non-mode7 pixels (probably plus a 1-adjacent-pixel-at-1x-scale buffer) while retaining the high-resolution mode7 output.