This is not a practical request. The Map Counties feature does not return any geocaches, so there would be nothing to add to a vGPS or bookmark. All it does is show you the county boundaries.
To download all caches in a county, region or country use Map Compare. Just select yourself, no need to add a second person to compare with.
If you wish to map an existing vGPS then from the vGPS page select export > Map List.