I lift up a oranment and let it wiegh down the zuchinni I put in there. If it's baby pleco's, I just put some gravel in the middle of the piece, and eventually the baby's knock it away while they are eating, and the zuchinni stays at the bottom.
If it's a small portion just microwave it in some water for about 3 minutes, you just have to cool it off before you put it in the tank. Always does the trick for me.