Can I add <% @Register TagPrefix.....%> by code using IToolboxUser?

[Luis Ramírez]

Hello,
I would like to know if can I emulate what visual studio does when I drop
a custom webcontrol from the toolbox. VS automatically add the <% @Register
TagPrefix=".....%>.

I found that VS calls IToolboxUser.ToolPicked in order to do this. However
when I call this method nothings happen and when I call
IToolboxUser.GetToolSupported always returns false.

I would like to know if what I trying to do is possible?

Any help will be appreciated.

Luis Ramírez.