It's interesting you say that! My pullets pushed the golf balls that we put in the nesting boxes before they started laying and even now they will push them out. I switched to Easter Eggs about two days ago and not one has been pushed out. In fact, I've found a few pullets laying on them! You may have a hard time finding Easter Eggs this time of year in the stores but if you have any on hand it's worth a shot!
Are you able to go out and collect them on an hourly basis or so? Also, they may be getting bored or not getting enough nutrition from the feed you are giving them. Try taking out treats to them and switching food. Or maybe try hot sauce inside the eggs you blow out instead of the mustard they like. Sorry I can't think of anything else!