You will probably not be able to do this with CSS Sculptor alone. You can use the presets that are included with SiteAssist pro that include the CSS Sculptor presets for this design.
Using these presets you can add this new nav area to the preset or create a new one based on this original.
Once you have saved the CSS Sculptor preset you can use this to generate a new SiteAssist Pro layout. You can then use this new layout in the SiteAssist Pro wizard to modify the existing site or create another.
We have a guide on how to do this in the SiteAssist Pro support page:
In the How To's there is a document for customizing your SiteAssist Pro layout.