Low quality billboards in terrain, any way around it?

We have quite a lot different tree objects defined on our terrain and it seems that the billboards used by the terrain engine is using a shared texture for all billboarded trees. This means that the more different tree prototypes are defined for a terrain, the lower quality the billboarded trees become. Is there an option to increase the texture size of the billboard texture?! If not and UnityLabs is listening, please make it possible to have higher quality billboards!

example