Soapbuddy's right the freezer is your friend for that stuff. But if that doesn't work, just remember to make them well ahead of time and let evaporation pull them from the sides.
You know, I deal with this problem way too much to still be dealing with it myself....hmmm...I bet there's a spray teflon we could get at a hardware store to lightly coat our teeny plastic, multi-cavity molds. I use such molds for painting embeds, so I don't want anything coming off on the soap like oils and such. I will call the hardware store tomorrow, maybe I can even find a teflon-type spray that is food safe (so we'd know it's not coming off on our soap). *makes a note*
PJ,
http://www.pjsoaps.com/1New.html