How to tell if a web control can accept dropped controls

[KCS]

How to get parent/controldesigner of STANDARD webcontrol

Hi there. I need to determine, at design time (programmatically via
IDesigner?) if a control on the web form can accept dropped controls, so that
I can display a design time dialog showing the names of the controls you can
drop other controls on to.

So my question is - how? Is it possible to determine / access the parent
control designer or control designer for a control you did not author (such
as standard panel control) without having to create a control that inherits
it? Or is there some property or method not obvious (via WebControl?) that
shows this?

Thanks for any help, Kevin.