I'm starting an experiment next week with a marketeer, where she can work whenever it suits her for how long she wants for a retainer/fixed amount per month. The rate is about 1/4th of a full-time freelance, and the idea is to mutually agree on actions and/or outcomes/results each month.
I plan to do something similar with a very senior dev this summer, who is training for a triathlon and has 2 small kids he needs to look after, probably at 50% of market rate...
The biggest issue when setting up something like this is trust, but as I've worked with both of them before on short stints with a regular daily rate (a few days to weeks), I don't have that issue myself.
For me it's a simple math equation: how much am I putting in, and what will this bring me financially (SaaS license income etc), so I can easily figure out the point where I'll be satisfied with our agreement.
I have high hopes for this experiment, but low expectations. We'll see how it goes.
My best bet for you would be to look for similar opportunities: find someone who pays on commitment/outcome, and doesn't care about hours worked...