I am trying to figure out if I can make one of the radio button choices a default, but is not possible on Google Forms? https://www.google.com/forms/about/
Is is not possible even with the Google app script?
You could use the option to pre-fill a form and set up the defaults you wish - leaving other fields blank. Then share the link to that pre-filled form rather than the original.
You can do this either using the menu options from the form editor, or by constructing a formResponse in google apps script.