I don’t know about AE 7, but you can do this with AE 6.5. The problem is that After Effects is grabbing the output device for itself and not letting go – so you need to disable it before going into Color Finesse (as well as having the appropriate preferences set in CF). The keystoke to toggle AE’s video output is: Command + / on the numeric keypad (mac) or Ctrl + / on the numeric keypad (windows).
So just disable AE video preview before launching the Color Finesse interface, kind of a pain, but it should work.
Hope this helps,
-Kurt