This is actually incorrect. Unfortunately you need two or more to do the trick because in order for it to work and multiply you have to select, let's say an elixer, once and choose someone to cast it on and then select that same item again but cancel everytime before you select someone to cast it on.As for Dazers, there's a dupe trick if you have the W Item materia. Something like select to use it and cancel upon the second select to dupe it nonstop. You can even do this with only one dazer, do something like select an item to use on a character, select dazer, cancel, select dazer, cancel, and num goes up.
I just tried to do it starting with two seperate items but it doesn't multiply so I'm assuming the reason the glitch works is because it's reading the same item getting canceled multiple times.