Mike Manes, W5VSI has designed a fast release mechanism that senses the loss of support from a balloon just after it bursts and then releases the support line immediately or very soon thereafter to significantly decrease the possibility of the remains (shards) of the balloon becoming entangled with the rest of the payload line and especially the parachute.
Here is a presentation Mike prepared for the GPSL 2006 event. The last few slides show the release mech.