I have and its not that hard. I've split X2 colors equally between the original 4 ounce bottle and a new one, then fill to the bottom of the neck with raw plastic, add 1/4" stainless nut to each, cap and shake. This works well for the fluorescent colors which seem to come real thick. The resulting colors are still very potent but instead of having to use say 6 drops in a 4 ounce batch with the pure X2 I need to use 8. Also, the colors tend to be way more transparent, something I like. I do not cut every X2 color, primarily the fluorescent.
I'm not measuring in any exact sense here so basically every bottle will have its own drop count curve to learn. Because the raw plastic is used to cut the colors it is super important to shake the bottles well before use and to be certain that the colors go into cold, raw plastic at the beginning of the recipe.