good point here about disposing pieces of plastic in the ocean!!!
the problem with using a swivel is it leaves a trail of bubbles behind it which the guys in the know say is not good( prob other fish hit it - not sure)
if u going to use one, simple make a fold in the line(u shape) and tie the balloon over the double line fold, when the fish takes, the balloon pops and if the line is not straightenned out disposing of the balloon, u can easily remove it urself when the line gets back to the boat. trial and error mate!
again chance of polluting the water, so try and refrain.