one sided geometry - problems with lightmass


I have a problem with the lighmass on a one sided plane. The back side of the plane is appearing as not lit. I’ve checked the UVs and there is no overlapping. I use the 2 sided foliage shading model. I’m sure that the problem lays in the lightmass, since I’ve tried every other shading model and blend mode. Also the lightmap density is set to 512 (which is an overkill anyway).

I’ve found a workaround, but that includes that I model the back side (so the leafs are not single planes anymore), but this workaround is a lot messier and more time consuming.

Is there any way to let lightmass know to light up both of the sides of the planes equally?