I currently DO have kidney problems so I don't take the epson salts. I make sure to crush the stones before I flush by drinking apple juice, taking malic acid supplements (the ingredient in green apples that dissovles stones) and lately I've been trying out Gold Coin Grass from www.sensiblehealth.com. I think everyone should prep for a flush whether they use the salts or not, but it's especially important for people who do not.
As a compromise, you can do the prep and lower the dosage of the ES to just one glass of one level tablespoon. That way, you get the benefit of it opening the bile ducts, and can use something else less stressful on the kidneys for the laxative effect.
there is an alternative kind of magnesium you can take but who knows if it does anything besides act as a laxative, so really any kind of laxative will help. Plus magnesium can be as difficult on the kidneys as salt, since the kidneys regulate all electrolytes.