Can you explain what you mean by culling in physx?

AFAIK, physx doesn't cull anything, and it would be stupid to do as it would disable parts of the, well, world, and it has nothing to cull from, like a camera/viewport, are you referring the actors sleeping?

Edit: Try to give us an example of the problem, maybe there's an alternative solution.

-MIGI0027

Further down on that page this is precified:

It is also possible to generate hits for both front-facing and back-facing triangles of a mesh, using 
PxHitFlag::eMESH_BOTH_SIDES flag. A mesh is treated as double-sided if either 
PxHitFlag::eMESH_BOTH_SIDES or 
PxMeshGeometryFlag::eDOUBLE_SIDED is set, so a mesh with eDOUBLE_SIDED flag will always be treated as double-sided regardless of whether PxHitFlag::eMESH_BOTH_SIDES is set or not. If a mesh should sometimes be treated as single-sided and sometimes as double-sided, create it as single-sided and specify PxHitFlag::eMESH_BOTH_SIDES for the query, or set it in the hit filter callback.

So you could disable this culling by specifying PxMeshGeometryFlag::eDOUBLE_SIDED when creating your geometry with your actor.