(Out of entertained lurking) I actually use the lid to pop those caps off if it already has juice in it that way I don't get messy (now I like messy, but not so much with e juice). To do it, unscrew the lid but don't remove it from the bottle, then give 'Er a sideways flick of the wrist and the little cap should pop right into the lid. I do this if i am blending one juice with another or adding flavor to a juice i have already made. If you keep the cap inside the lid, then when you are ready to put it back on, simply put the lid back on and screw it tight- the inside cap will pop back into the bottle, and you never had to touch it ( or lose it, which is the real reason I started this technique)
(Pause for glowing praise of the OP....)
Bravo on this thread- it was exactly what we needed to decided to take the leap!