I don't know, maybe it depends on the specific size of one' fingers, but when I want to switch between picking and fingerpicking I shift the pick from the picking position to have it wedged in between the two middle knuckles on the inside of my right middle finger. If you do it a few times it becomes second nature. If you adjust your hand position based on where the rather limited middle finger now is, you can combine it with the index and ring and chicken pick or double or triple stop as much as you want. (Never have learned to use the pinkie on my right hand...)
Dropping a pick is a foreign idea to me... never saw Jerry drop one... don't recall ever dropping one myself either. Doesn't make me Superman, but how hard is it to hold on to a pick? I meean, how often do you drop a pen or pencil when writing? If you drop a pick more often, you are writing too much and playing too little. (And, btw, Jerry held a pick as if he were writing with it, at the tips of his thumb and first two fingers, as opposed to the conventional flat of the thumb/top edge of the index finger grip. I don't, so maybe that's why I can't play as well as him
) Just sayin'...
I think most of those pick-holder rigs are for grabing a new pick if you rough up the edges of the one you're using too much. Least, that's the way I've always seen it.