It would require external components. To summarize the "problem" with wiring diagrams from the AIU and Platform manuals:
The two control methods would give conflicting signals to the platform when they disagree. By disagree I mean the DCS remote saying passengers arrived (visible) while the manual controller saying passengers departed (hidden). Or vice versa.
So you need some form of external arbitration.
1) A DPDT toggle switch can select whether the B and C terminals on the platform are connected to the AIU port or the controller box. Set the toggle switch to select who is in control. A toggle switch is maybe $2-3.
2) A relay can arbitrate what the Platform is to do. That is, you first decide/specify what to do in case of conflict. If one says "departed" and the other says "arrived" which do you want? The relay is wired to send that command. Obviously if both controls agree, then the relay sends the unanimous vote. A relay with supporting components is maybe $5.
I can draw a wiring diagram for either or both methods if my understanding of the "problem" is correct. It would be useful to know if soldering is off-the-table and/or your general comfort level with wiring and the like.
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Separately, this reminds me of the classic problem of having two ITADs controlling crossing gates (the ones with 5 wires). You want the gates to drop with a train approaching from either direction. But you get conflicting commands if only one of the ITADs is triggered. In this case, the arbitration logic is obvious - gates go down if either (or both) ITAD is triggered! In this case you have to use method 2 (a relay). There have been several OGR threads on this.