Aside from contract work, I think you've pretty much limited your choices to consultant or commercial fisherman.

Even consultant is tough. You have a business that you need to run and typically can't just disappear for 6 months at a time and largely ignore everything going on in the industry.

It's actually almost certainly easier to consult part-time (whether you intend it to be part-time or not!) than it is to go 120% for 6 months and then rapidly ratchet it to zero for another 6.

I think the only person I know who has done something like this was a lawyer who worked as a contract lawyer for some big finance company (I think) for about half the year. Which doesn't sound like a bad gig. But it's hard for most white collar jobs.

Ski instructor? Mine site commissioning engineer? Game developer (except you get the rest of the year off because you got fired when the game shipped.)