I’ve done a bit of research. It seems GRID & Quadro Virtual Datacentre Workstation are two different product. This[3] link states “When you select a GPU for a virtual workstation, an NVIDIA GRID license is added to your instance.” Based on that statement & these pages [0][1], it seems they are two different products requiring two distinct licenses.
If the GRID vPC features are already available, it would seem the license is added without user interaction, & that the GRID vPC product is what Google provides.
If there would be a license on the machine that would allow you to activate the Quadro Virtual Workstation, this doc [2] provided by NVIDIA will guide you on how to find it. Let us know if you find success.
[0] https://www.nvidia.com/en-us/design-visualization/buy-grid/
[1] https://images.nvidia.com/content/grid/pdf/161207-GRID-Packaging-and-Licensing-Guide.pdf
[2] https://images.nvidia.com/content/grid/pdf/GRID-Licensing-Guide.pdf
[3] https://cloud.google.com/compute/docs/gpus/#gpu-virtual-workstations
This[0] video provides a visual tutorial for NVIDIAs licensing setup.