The problem with support items was that they could be (ab)used by non-support players or potentially even the supports themselves to generate more gold per minute than was intended.
The solution therefore is to not allow this to happen. Return the charges to the final items and just have a constant minion gold debuff applied when such an item is in a players inventory. Doing the math this works out to about 60%, so anyone with a support item only ever gets 60% of the gold from any minion kills, at all times. This way, if a laner wants to take the support item they can, but they will have to use it to full effect just to break even with the gold they would normally get from minions. It also prevents supports from generating more gold per minute than laners under any conditions.
And to be extra safe, maybe change the stats on the items to be more appealing to supports and less appealing to carries.
Tada, support items can no longer be abused, and supports can have their income back.
Bonus QoL suggestion: switch the targons/execute passive on the "tank" items to the coin passive upon quest completion.