UV flipping and normal mapping

Unity 5.5 has added the useful feature of UV flipping to add variety to particle effects but flipping UVs breaks a lot of normal mapping techniques. When UVs get flipped it also flips the direction of the normal mapping creating flaws in the lighting. At the moment I have not found a way to detect UV flipping in a shader and correct for it. could a 0 - 1 value be passed along with the UV to indicate if a UV for a specific Particle Has Been Flipped and what axis the flip has occurred on.

 

The issue with ddx(uvx) is that it does not work in the vertex function or on low end mobile and to get the best performance out of a particle shader you want to offload as much work as possible onto the vertex. My current normal mapped particle shader does almost everything in the vertex function and has only 4 lines of code in the fragment function.
The random number idea is a good one though I will try that out.