|I was trying to run a relatively short piece of narrow (1/4") elastic through a narrow, very long casing at the top of a gathered bodice. PR member goodworks1 directed me to an idea posted a couple of years ago by another member, pittysmom (http://sewing.patternreview.com/cgi-bin/review/readreview.pl?ID=821), which is to use a large plastic yarn needle to pull the elastic through the casing. I did a variation on this technique -- I threaded the elastic through the eye and tied the threaded end in a secure knot just under the eye of the needle.
But that's really just a variation on someone else's tip. My own tip is this -- to keep from losing the elastic as I pulled it though the long casing, I tied about a yard of sturdy yarn to the other end of the elastic (the free end). I was able to run the elastic through the casing in a matter of minutes -- and with no worries about having to fetch a lost end!
P.S. Since the ends of the elastic may get a bit gnarly when you tie them to the needle/the yarn, you might want to use a couple of extra inches of elastic (it may help to make a mark on the elastic to remind yourself what the suggested elastic length is for your size).