see http://forums.arcgis.com/threads/26907-DDP-Can-extent-indicator-frame-zoom-like-the-primary-frame-do...
It's still the same procedure. You don't have to show an extent indicator to use that data frame extent option.
Open the properties dialog for the second data frame, the one without Data Driven Pages and select the Data Frame tab. At the top of the dialog, Extent dropdown, select "Other Data Frame". Then you will see various options for how you want the current data frame's extent to be driven by the other data frame. Set the margin to 100%.