pmic: to answer your question it's a pretty simply mechanism.  Your lewis acid coordinates to an oxygen lone pair, which facilitates an SN2 type attack on the methyl group by your nucleophile.  You need either a very strong acid, a very strong nucleophile, or both.  I wonder if a phenyl thiolate would be strong enough to affect the demethylation with a weaker lewis/bronsted acid?

edit: a thread on sciencemadness notes the following:

Attempts to demethylate eugenol to obtain 4-allylcatechol in one step were made. The demethylating agents used were hydriodic acid, pyridine hydrochloride, anhydrous aluminium chloride, sulphuric acid and potassium hydroxide. However, in each case a polymerized product was obtained.

It seems to me the lithium chloride method on the first page (and on rhodium ages ago) is going to be the best way to go as far as "OTC" is concerned.  Not to mention you might just be able to lead a tube from the reaction pot to aqueous NH3 to get a nice MeAm solution   Unfortunately it seems the solvent is quite important

Lithium chloride-catalyzed selective demethylation of aryl methyl ethers under microwave irradiation
Fang, Z. Journal of Molecular Catalysis A 2007, 274,16

First we investigated the solvent effect on the cleavage of aryl methyl ether under microwave irradiation. 6,7-Dimethoxy-2H-1-benzopyran-2-one (compound 1) as model was irradiated by microwave in different solvents with LiCl as promoter. DMF was the most effective for this cleavage, but the reaction hardly proceeded in water, ethyl acetate, declin, xylene, or toluene. The reactions carried out in dimethylsulfoxide (DMSO), tetrahydrofuran (THF), or acetonitrile resulted in formation of trace cleavage products after a long time (1–2 h) under microwave irradiation. The solvent effect on the reaction may be linked with the solubilities of 1 and LiCl in the solvents.