The link still works for me. I think there are a few threads about this, try searching.
In general you just manually maintain a second Collection that is your normal map. Disable trimming on both and add the sprites in each Collection in the same order. Each time you update the normal map collection you need to manually set compression method on the resulting atlas texture to 'normal map'. But you can modify tk2d code to add this as a choice in the compression drop-down quite easily.
Sprites meshes need normals and tangents, currently I think this only works for standard sprites (and not tiled/diced/tilemaps) so you need to put your own generation code in if you want those to work.