I don't see how Epsom salts can help BER, as it is a calcium issue, and Epsom salts are magnesium. If the problem is with heirloom varieties (non-hybrid), the answer is that we just have to deal with it... many heirloom varieties root structure is not sufficient to bring in enough nutrients for the plant once it gets really going - this is (one of the reasons) why heirloom tomatoes can be expensive in the store since up to 50% of the crop can wind up being not saleable. Also, since Ca is not very mobile (it is moved by the plant with water flow due to transpiration, not actively by the plant itself), conditions that limit transpiration like high humidity or cool temps can exacerbate the problem.
In order to fight this in a garden, you can make a foliar spray using CaMg, a good source of calcium. Spray on the leaves closest to the fruit - maybe you can even spray the fruit - I'm not sure if that works or not... but you have to spray before BER takes hold - it is irreversible.
ETA: the crushed eggshells are a source of calcium, but are not directly absorbable - it must first be broken down by fungi and bacteria to the salt form so that the plant can take it up. So it will take quite a while (maybe for next year?) for the eggshells to make a difference.
