Grid for unstructured data in separate file?

to save disk space when writing time-data on a constant unstructured grid, it would be nice to write grid points and cells once in a separate file and reference this file in the subsequent .vtu files? Is that possible? Or is it possible to write the grid data in a .pvd file where the .vtu files are referenced?

I really second this request. @janlv, did you find something ?