A lot of people have complained about the fact that folders stored in the Dock automatically work as Stacks. One possible way to get around this is to use saved searches instead.

If you can create a saved search with the items you want, you can add it to the right side of the Dock, and clicking on it will open the saved search in the Finder, instead of displaying a stack. Although you can change the icon of the saved search, all saved searches have a file extension of .savedSearch, and you can't remove it.