Buy the ZED fare from your airline while you are here. If you don't use it, it should be fully refundable, or if you don't use a part of it. For example you fly one leg, then are able to JS on Delta back, the rest of your ZED on the carrier you booked it on should be refundable.
When you buy the ZED fare they will ask you where you are going and what airline you want to buy the ZED fare on. Tell them what airline, where you want to connect, etc. etc. You can list on
www.flyzed.com or you can usually call the airline to list as well ahead of time. Good luck.