Get to a level of skill and track record where it's easy to find companies willing to hire you. Then, when negotiating, give up significant salary to reduce your time commitment. It works better with smaller companies (Google, etc are not going to go for this)

Join Google - it allows part time work (50%/60%/70%/80%/90%) and people do use it creatively to maximize their convenience. At or above 50%, you also get health insurance. Perks stay the same.

It's 100% negotiation. Nobody is going to give this to you.

The way to get these out-of-the-norm gigs is to get good—so good they can't ignore you (to quote Cal Newport) or in this case that they'll say no because they need your skills.

If you get good and are known to be good, you can ask for any kind of work arrangement.