Keep Support-Item passive for 5+ minutes after selling the item.
Support players won't mind and it screws with all those fancy tactics that resulted in the support position being negatively affected over the last few years. Why bother nerfing/buffing/reworking tons of champions and items when you can just say "if you want to pretend to be a support then stay one for a little while longer <3"
I can't see any situation that would make me want sell my support item aside of maybe an epic last stand against a superior enemy that can only be defeated - maybe - if I free that last slot for a better item. Even if that situation accours you have enough money to not give a flying fuck about minions anyway.
So for everybody selling the support-item, a passive should be added that lowers the gold gained from minions for a further few minutes.