Foliage casts no shadow when viewed from a large distance

Hello. I recently placed trees in my level using the foliage tool.

These trees have a billboard as their last LOD, which is fine for performance.

However, when I go far enough from them, as they become billboards, their shadows on the landscape dissapears. Is there a way I can keep those shadows, while maintaining the billboards? Maybe baking their shadows on the ground, is that possible?