I figured there are enough jewelers on the forum that this trick is worthwhile passing on. I've done it with a string a couple of times and also with a finger ring saw through the years. But, this is even easier. You can buy the same narrow elastic from any fabric shop and would be worthwhile having just in case.
[video=youtube;DxoAbK5Pc6w]http://www.youtube.com/watch?v=DxoAbK5Pc6w[/video]
[video=youtube;DxoAbK5Pc6w]http://www.youtube.com/watch?v=DxoAbK5Pc6w[/video]