How to mirror-tile a normal map properly?

I have a normal map that has it’s tiling set to mirror. That means every other tile of the texture is correct, and every other has flipped / incorrect tangents. I was about to correct it in the material by manually flipping every other normal tile’s channels, however, I wonder if there’s a better way to do it by toggling some switch somewhere etc.

Well, I don’t think that this is possible, at least I have never stumbled uppon such a setting…