How can I get 3D Buildings to clamp to Cesium Terrain

Hi everybody,
I was wondering if anyone can help me with clamping 3D Building Tiles to the Cesium World Terrain.
We are developing a 3D web application with Cesium JS and we need to have our 3D buildings sit flush with the Cesium World Terrain. Our input into the application are 3DTiles. I know you can clamp citygml files to the terrain with the in-built clamp to ground tool in Cesium ion but is there any way to get 3DTiles clamped to the ground in cesium JS or with the help of FME?

We use FME to create our 3D Tiles but we have not found a way to get the buildings to line up with the terrain.

I would really appreciate some help on this!

Thank you,