Steve, Are you familiar with transdermal magnesium therapy? It uses a concentrated magnesium chloride derived from sea water either applied topically or used in baths. It is excellent for easing muscle cramps and other forms of pain. It does not interfere with fasting and is very safe. You can find out more by going to the Magnesium forum. You could use Epsom Salt in baths, but the Epsom Salt is not easily absorbed on a cellular level and works better in a detox bath or as a laxative. I got my magnesium oil from Global Light Network, but there are plenty of sources of Mag. chloride also called Nagori (sp?) or magnesium oil, ust do some searching.
Oral supplementation is not a good idea with any kind of fast. It really defeats the whole purpose of fasting.