I know this isn't what you asked for, but it might work.  
I have found the organizational chart to be too limited
for most purposes.  There is supposedly a way of
constructing a flowchart in Word, but I have never been
able to find the connectors, and the available information
is enigmatic even for Microsoft.  However, Excel might
offer the functionality you need.  In Excel, click View .
Toolbars > Drawing.  On the Drawing toolbar, click
Autoshapes.  You should see Flowchart and Connectors.  Use
these in combination to get pretty good flexibility.  You
could check Word in the same way to see if Connectors are
included with Autoshapes.  If so, you should be able to
use Word to make your flowchart.  If not, complete it in
Excel, group all of the elements together, and copy and
paste the whole group to Word.  You will be able to edit
the text, add text boxes, etc. (everything except add
connectors).