Using UI textues authored in Gamma space in Linear mode

I would like to use UI textures authored in gamma space on linear mode. I found some information at this QA, but it seems that it didn't solve the problem.

https://answers.unity.com/questions/998820/ui-created-in-gamma-color-space-does-not-appear-co.html

The shader code mentioned in this answer did not solve the problem in my experiment. Appropriate alpha value changes according to RGB color in linear space blending. See the image below. This is more obvious when the background color is white.

Also, AFAIK, There is no practical way to reauthor linear texture with alpha channel in Photoshop. Our artist told me that we need to use AfterEffects or Nuke for reauthoring content for linear blending.

Does anyone knows any good way to solve this problem? I hope that Unity supports a feature that allow us to render UI in gamma space whether color space for 3d rendering is set to linear or not.