Unless you can do something to bypass the button on it, it might be easier to just get a new humidifier - I have one like this, it doesn't auto shut off once you switch it on using the dial. I find the design a bit unwieldy and I don't really like it, but it has worked well for about two years now.
https://www.amazon.com/gp/product/B00J4LN490/ref=ask_ql_qh_dp_hza
I have seen people use pool foggers too but I don't have any experience with them (although I do like the lights!)