Wire it to an aprilaire 60 control and set it up for blower activation. But as others have said it works much better when the heat is on.
Buy this: https://www.amazon.com/Aprilaire-60-Humidistat-Blower-Activation/dp/B0085YQUVQ/
And install it according the instructions. Then you will have blower activation (it will run the fan when the humidifier needs to run). Install the outdoor temp sensor for best results.
One change, on most newer equipment you can run G right to the furnace instead of bothering with rerouting the thermostat G signal through the humidistat. So leave the thermostat wires alone on the furnace and just add the ones for the humidistat to the terminals.