I'm confused...
Are you talking about adding files/folders under 'Devices', 'Places', and 'Search for'? If so, that's old news.
Here is another tip:
Personally, I hate the stacks feature on the dock. I would rather click the icon and open the folder in Finder (grid/fan view just doesn't cut it). All you have to do is create an alias of the folder and then drag it to the dock. To make things clean/simple, I keep all the aliases within one folder.
I hope that helps at least one person (took me a week to figure it out).