You can forget the ES and replace it with magnesium tablets or powder. I buy a powder here in Vancouver, Canada from a health minded pharmacy. I take 1 tablesp. instead of 1 ES dose, that works for me. You should be able to buy magnesium powder or tablets in a health store.
You could also use a liquid produt from a drug store called 'citro-mag' its a magnesium laxative, it comes in a 12 oz. bottle which you could devide into 4 doses. Citro-mag tastes like sparling water.
citro-mag requires you to drink a lot of water, about 1 cup every hour. I have liquids until 1 hour before oil time and again about 5 hours after the last of the oil, no problem.
Let me know how it goes. Giz.