Repeating Images From an Atlas

Hi I think this comes under the "Cant be done" Category but thought id ask.

I'm experimenting with a tile system using the single mesh of many quads approach. and Assigning the tile texture to each quad based by setting the UV cords to match the Tile Image in an atlas.

I'm thinking of using this approach for 3D Wall geometry however where as a quad only takes up 4 verts per tile a cube with all but the bottom side being visible will take up 20 (5 quads).

I would like to optimise this by combining "3D Tiles" so if 3 cubes are touching I only need to make 1 double length oblong [_][_][] -> [] so instead of 60 (44 if we remove the touching faces) verts (15/11 quads) I would only ever be using 20 verts for any length of wall.

However since I'm using an atlas I'm stuck with 2 options when it comes to setting the UV's either I stretch the one image across the entire face, or I end up with the first "tile" correct then subsequent tiles will display the next images along the faces axis.

The only solution I can think of is to make my atlas Vertical only so the tiles can wrap along one axis at least but this limits the number of tile images I can store in a single atlas (1024x64 = 16 64x64 tiles).

I can use multiple materials but then I'm adding extra draw calls and have to update the triangles every time I change to an image outside the current material.

So can I wrap a image/sprite inside an Atlas Texture? If not is there a better solution than the above?