[GTJIM (R.I.P.)]

Maybe a look at an idle speed increasing solenoid like the ones used to up the idle speed when the air conditioning unit is turned on would help. Wire it up so when the headlights are turned on it is activated. Have a look at some of the later model cars with air conditioning to see how this works - the solenoid is usually located in the fuel injection accelerator linkage area on the motor.