If you add one of those basemaps to your ArcMap session, you can right click on the "Basemap" group layer on your Table of Contents and save a .lyr file to your system somewhere. (Use the "Save As Layer File..." button) Then you could run something like this in your script to add it to your map.basemapLayer = arcpy.mapping.Layer(path_to_your_basemap_lyr_file)
mxd = arcpy.mapping.MapDocument("CURRENT")
df = arcpy.mapping.ListDataFrames(mxd, "*")[0]
arcpy.mapping.AddLayer(df, basemapLayer, "BOTTOM")
Of course, the downside to this method is you'd need a copy of the .lyr file for that basemap somewhere on your system.Matt