When at a pond that requires throing Rupees or an Item into it, toss an item in. Afterwards, continue to stand in the same place so that the text box comes back after a short waiting period. If you happen to start throwing your boomerang when the text comes up, it will be frozen in place. The boomerang must be still in your hand for it to stay put. After the text box closes again, you can move around and the boomerang will stay in place until you hit it with your sword.
Submitted by: Artemis251