there is no extension for sidebars yet. however, the sidebar code from 3.0 will work on 3.1 styles
in order to use an extension and do it properly, you could install the custom code extension and use that for your sidebar.
I'm baaaaaccckkkk. still doing work on donation basis. PM your needs.
Premium phpBB 3.3 Styles
If nobody is in the forest, does a tree really fall?