Maybe if you create textures that have 4 'quadrants' with each being a smaller scaled texture and then you can specify texture AND quadrant to use on texture -in other words the texture is 512x512 and you tell shader to use the upper left 128x128 block for pebbles but the whole texture for another area?
You can see a texture here where I mixed 4 different textures. Could have as easily made much smaller scale in one area.
