I've heard some people say to put a small hole in and some people say not to.
I would have thought if you do it could ignite,especally with a metal object,wouldn't it short? That's why i' saying i'd ask FMA what to do.
EDit: OK here's the FMA safety blurb
http://www.fmadirect.com/support_docs/item_1197.pdf on page 4 is the disposal instructions,says discharge then puncture 'the plastic envelope' so i think that means just the outer so the salt water can get to the tabs,and not the cells.
Here's a thread on wattflyer about lipo disposal,
http://www.wattflyer.com/forums/showthread.php?t=5840