Well, it's possible to take mushrooms all the time as long as you have plenty, your tolerance will soar. I wouldn't say it's a good idea though. Your poor mind will become one with the mushrooms. I've met mushroom casualties before and it's not pretty. Oh no.
Mushies definitely have an integration period that can't be put off indefinitely. There's no number to say what an individual can deal with though, some of us are cool pushing the envelope far whilst others have a meltdown after a single dose. Mindfulness is required.
Hope your friend can find a way though. Living with pain is super hard and I totally understand looking for solutions that aren't textbook.
The nearest we ever come to knowing truth is when we are witness to paradox.