The only way I've seen this done in the real world requires the person to pick one primary job that always takes priority. The other job (or jobs) are targeted

The only way I've seen this done in the real world requires the person to pick one primary job that always takes priority. The other job (or jobs) are targeted at companies that go out of their way to be super "nice" such that they won't question someone being constantly unavailable. Without giving too many specifics away, the one case I discovered was with a person who claimed to be dealing with some personal/health related issues that required us to be flexible with their schedule. If I'm being honest, it worked on us for a while because we're sympathetic, but eventually the underperformance crosses the line into something that requires medical leave / short-term disability, at which point they gave up.