If one ammends the link YH provides from
https://accounts.google.com/o/oauth2/auth?client_id=YOUR_CLIENT_ID_FROM_GOOGLE_DEVELOPER_CONSOLE&redirect_uri=urn:ietf:wg:oauth:2.0:oob&scope=https://www.googleapis.com/auth/analytics.readonly&response_type=code
to
https://accounts.google.com/o/oauth2/auth?client_id=YOUR_CLIENT_ID_FROM_GOOGLE_DEVELOPER_CONSOLE&redirect_uri=urn:ietf:wg:oauth:2.0:oob&scope=https://www.googleapis.com/auth/drive.readonly&response_type=code
then the resulting access token works with the websave command in my question, so long as the client id and secret are from the credential type 'Desktop', as created in the google developer console. I had previously tried this approach, but with the credential type 'TV and limited input', as that was the only type that worked with the RunOnce function in the matlab2sheets FeX submission (n.b. the readme for that function says to use the 'other' type, which is now unavaliable). One can save the acces_token as a .mat for future use.