Can I do FTP/ERG workouts in course mode so I have to hold my own power?
Yes. You need to enable the option to show the course checkbox on the main timer. Go into Studio's options and into the Workout Options section and General tab. Enable the option to "Show the Course Mode option when doing FTP/ERG workouts". Apply those changes.
That will then show a Course Mode checkbox on the main timer when FTP/ERG workouts are loaded.
Check that option at any time before/during the workout and the trainers will go into course mode rather than FTP/ERG mode. You are also given the option to set the slope/grade% for all rider. Once set, you then have to hold your own power load.