Drive LEDs from a second source
You can put an LED in series with the opto-coupler LED, no other components required.  It won't increase the power consumption at all.

It will increase the minimum voltage slightly but would still be within your 12v minimum voltage requirement.

From your resistor values it looks like the current through the opto-coupler LED is compatible with the required current through the illuminating LED.  What value is the zener diode?







simulate this circuit &ndash; Schematic created using CircuitLab