Mm, don't think that would cut it. The high pH water actually prevents the plant's uptake of other nutrients. Magnesium certainly absorbs through the leaves, (I use it a lot on my orchids as an additive to my foliar feed) but it wouldn't help the plant take up the other nutrients it needs from the soil.
Twelve teaspoons of Epsom salts finally reduced the pH of half a gallon of well water by one point. Not going to be able to do that too often, I guess.
