How to get mastery on a champion not in your main role

I have mastery level 5 on Caitlyn, and I often get her in aram. In aram I often get S ranks on her. Which I think is a waste, because I can't get mastery in aram. I want to get mastery on her, but I can't play adc to save my life, I never learned how to farm. My options now are: Spam adc games, often feeding due to lack of experience, and hope I get lucky games Or, play her in my main role, and hope I don't get flamed too much for Caitlyn support

Which do you think is the better option?