Could you soxhlet cactus chunks with, say, methanol and get good extraction? I wonder.
On paper there's no reason this wouldn't work, ethanol should dissolve both the freebase and mescaline salt, you could always add a little lime (Ca(OH)2) to force the pH up to ensure mescaline is present as a base.
Soaking it in acidic water is also a proven good way to do it, you form soluble mescaline acetate which is stable to boiling, you can just boil the cactus chunks for a day in lightly acidified water (lemon juice, vinegar etc) then strain (and optionally concentrate) to get a crude broth that is quite suitable to do extractions of.