Emulating Old Tektronix Coded Probes
According to the manual of my Tek 465B scope, the coupling ring is connected through a resistor to the base of a transistor that controls the illumination of the 1X and 10X LED indicators.  A typical probe (P6105) has an 11k resistor connected between the coupling pin on the probe body and ground. Thus when the probe is connected to the scope BNC connector, the transistor is connected to ground through this resistor.  This changes its state which then turns off the 1X indicator and turns on the 10X indicator. If you could take the Tek probe BNC (with the coupling pin) and substitute it for the generic probe BNC, you might be able to make the probe sensing work.