How do I specify the columns that should appear in a hover in a holoviews.operation.gridmatrix?

In the following, the hover simply shows the x and y values for each individual plot. How would I additionally show, for example, country in the hover for each plot?

from bokeh.sampledata.autompg import autompg
autompg_ds = hv.Dataset(autompg)

hv.operation.gridmatrix(autompg_ds, chart_type=hv.Points).opts(hv.opts.Points(size=2, tools=['hover']))