Unfortunately, this is close to impossible in my industry, and most others. You work 40-plus hours or you work zero.
I've mentioned this before but my company hires Rails developers for 24hrs/wk. Health insurance is provided and salary is proportional to full-time.
It's not for everyone, but it works well for us. Everyone's fresh and relaxed when they come into work, and the free time is great for learning, side projects, exercising, travel.
Anyway, we're actually hiring right now: if you're in the Bay Area and looking shoot me an email.