Creating a Tools Separator in Acrobat X Toolbar

I have an Acrobat plug-in which, for Acrobat X, creates a custom toolbar with AVToolBarNew and then positions it on the Tools pane with AVAppRegisterToolBarPosition. As I have a lot of tools on this I would like to group them with tools separators just like Acrobat's Pages tools does with "Insert Pages" and "Edit Page Design" separators.

However, when I try to create a separator with AVToolButtonNew it does not appear in my custom toolbar whether or not I try to specify some additional text with AVToolButtonSetLabelText or any other options. Are these the right calls or do I need to do something else to get what I want?

Thanks for any help.

David