You need to use some very fine point watch tweezers which can be picked up quite cheaply on eBay (looking at mine, size 5sa would probably do the trick). If you can get these in the crown tube and get a good grip on the stem, you should be able to press the release button and hay presto!
If you look around on the boards or do a google search, I'm sure you can find stem removal instructions with blow by blow pictures.
But as the sputim said, only do this if you feel confident.