I've never ordered from that vendor, so I haven't seen the bottles, but I think I know what you're talking about. The problem is that
juice doesn't come out on it's own, but if it were a plastic bottle that you could squeeze it would...
My total guess at a good solution besides prying off the cap and transferring to another bottle is this:
Take a paperclip or somesuch and heat it up really hot, then poke it
through the plastic cap near the edge. That will allow air to get in the air hole and liquid to go out the center hole. I think the problem is that the liquid can't get out because it's airlocked. Make a little vent hole for air, and problem solved. I think.
ETA: The other solution would be to use a syringe w/ needle or a small enough pipette/eye dropper.