How to make a custom or user control ready to contain controls dragged from VS tool box ?

Question

Hi All

I created a split container custom control as follows:

1- inherit from splitcontainer
2- add another split container (horizontal) to the second panel of the first container

question: how can I make the panels of the second split control ready to contain
controls dragged from the tool box ?
I can do that programatically but if you drag from the tool box,
ofcourse they gonna be pasted into the first split control since it is the
main container.

thanks for hints.

-moe