Sorry for a slow responce, we've been out to IBC in the past couple of weeks and still catching up. To answer your question: Justification button is global to the text object so you may not be able to mix different justifications in the same instance of Calligraphy filter but you can add multiple filters to accomodate this text effect. I'm sure you've figured this out by now, but just in case...
there is a way to do it and I Iearnt it from Philip Hodgetts (yes THE "Philip Hodgetts" ) I am happy to share it with you
The basics are to use Title 3D from Calligraphy and to put a right justified and a left justified tab so they form a center gutter. Note that you have to put a tab as the first character in the line for this to work.
the tip in essence, is to use the Tabs in Title Crawl (Part of the Calligraphy package) and set justify right for the left column and justify left for the right colum to two tabs that are just either side of the center.
In Title Crawl you click on the tab marker in the top ruler bar to change from the default of center, to Justify right/justfiy left.
Remenber that the first character on the line must also be a tab.