Scenario triggers to convert units

Sorry if this's the wrong place for this, but I started toiling around in the scenario editor and I wanted to create a way to give a player units and buildings of another player that he defeats. My first thought was to set up kings that would convert all units of their team to Gaia when killed, but the issue was that these Gaia units, unlike others Gaia units, are not converted by proximity to units like I hoped. I can't just make the units convert to the ownership of the opposing player because I'm making a 4 player map. Is there any way to make Gaia units convertable after being subject to the "change ownership" trigger effect or is there any other way to achieve this effect?