Wards Earn Gold Mastery
Could there be a mastery that passively grants gold for each ward you have placed? Gold could be granted per ward per 5 seconds, or per champion seen. It would give supports income, and encourage warding, especially at lower rankings, where players don't realize the importance of vision.
Edit: Some people have asked "Why not just reduce the price on wards?" The mastery would encourage effective ward placement, as well as better vision control; denying the enemy team income.