How to create a vtkUnstructuredGrid in parallel

Is it possible to initialize a vtkUnstructured grid in parallel? Ex: using OpenMP.
The InsertNextCell() method is definitely not thread safe, even if Allocate() is called beforehand.

If there was a SetCell(vtkIdType id, int type, vtkIdType npts, vtkIdType *ptIds) this would be possible, but there isn’t. Is there an alternative?