Hmm, kind of surprised that increasing the bounding box of your object affects performance that much, when they are currently only cubes.
Have you tried instanced static meshes?
I would investigate about those performance issues or check instancing before doing something so drastic as disabling frustum culling, feature that any 3D engine relies upon and can cause much heavier performance issues. If you want to do that, you’ll probably need to edit the engine’s source code.
@Mind-Brain She is talking about frustum culling. The feature you are talking about is occlusion culling. Quite different actually.