I found these two patents interesting;

http://www.freepatentsonline.com/5071874.html

That one's for l-carnitine magnesium citrate.

http://www.patentstorm.us/patents/4...escription.html

And that one's for potassium-magnesium-citrate. Both patents simply involve mixing the various ingredients in small amounts of water. (There's some heat involved, but it seems to be produced by the chemicals themselves, above a certain temperature, it becomes less effective.) I think mixing smaller batches at home, as opposed to large batches on an industrial level, would protect against this.

Both patents use magnesium oxide. Magnesium oxid and citric acid are pretty cheap.