Cameras can be set with masking bits that don’t render certain objects. You can also arrange for the camera to render without atmospherics (so not everything is covered in fog) although this seems finicky.
However, even with a 4096 texture, why do you need to zoom so far in to the minimap? Can you just prevent zooming in too much?
You can also use a number of textures – 4 wide and 4 high tile of 4096 textures would give you the effective 16000x16000 texture size. However, that’s a LOT of RAM to waste on minimaps.
I think the main question is: What do you need the minimap for, and why do you need to zoom it in so far?