Consulting / freelancing seems like it would be the best fit for what you're describing. As you pointed out that involves work to setup. You can pay someone to

Consulting / freelancing seems like it would be the best fit for what you're describing. As you pointed out that involves work to setup. You can pay someone to set it up for you. Typically they take 50%-60% of the the total amount. You can find ways of getting a larger portion of the cut but that involves more work (at least up front). To find these jobs open up LinkedIn and start responding to recruiters. Say something like "thanks but no thanks I'm happy in my current role. I have actually been interested in doing some freelancing in the X space. Probably about Y hours a week part time not during business hours." Some of the recruiters won't know what to do with that but a suprising number will, remember that big cut they get? Alright now one last thing here. Another option. Instead of consulting and working extra hours, consider studying a topic that you enjoy and other people hate. It also needs to be in high demand and pay well. Then go double your salary or whatever and not worry about working extra hours or filling out billable hour spreadsheets and so on.