I don't believe there is any way to disable the pass-through; as it is just that, a pass-through...without configuration. It is a separate Ethernet run to the AP. The AP itself and ports ENET1-ENET4 are configured through E0 (rear of AP). The pass-through port on the rear bypasses the AP configuration to the pass through labeled port on the front.
To accomplish what you are asking, you can either not plug in an Ethernet wire to the pass-through port on the back of the 93H; or make sure that drop is on a different VLAN or just not patched in at the switch.