How to access custom JPanel in design time?

Hello everyone. I'm a greenhorn with netbeans, so don't be too hard ;)  

I have a custom JPanel which is a simple bunch of JLabels, JButtons, etc. that are placed on standard JPanel.
Let's call this class CustomPanel. I added my CustomPanel (customPanel1) as a new component to JFrame via
NetBeans IDE. Everything is just fine except one little thing. I can't add new elements to my customPanel1
via NetBeans IDE in design time. You can easily add elements to an instance of JPanel in design time, so i
guess it is obviously posible to create JPanel's child with such abilities. What should be
overriden/added to make it possible?

Thanks in advance for any useful advice.