Full Build Can't Buy Control Ward
Seeing that vision is important perhaps it can go to the trinket ward slot when it gets purchased with a full build. Then when you've use it, it switches back automagically to your ward/sweeper or w/e you had there before buying the control ward.
and other vision items (such as
line) should get a second slot called "vision slot" where you have your normal trinket (Stealth Ward or Sweeping Lens) then in the "vision Slot" you can have