so, basically, you want the option that's already planned to be in the game (volunteering as a test subject instead of being the doctor) except you want the player to have the option to swap out of their doctor character (having them go off and do their own thing) and take up the role as a random volunteer separate from their doctor character?

am I understanding this right?

that's actually an interesting idea, having your doctor character be a separate entity that goes around doing things while the player goes in as a separate character to be a volunteer subject. You've got my upvote.

not even for the sake of testing, but just having a crux there as a stereotypical mad scientist would amuse me greatly.