I wondered the same when I got my AA power boards... So I modified...
If you cut the track coming from the battery +ve with a knife you can then connect a feed to your switch from the battery clip. The switched feed can then be reconnected to the circuit via one of the tabs on SJ1. SJ1 is used to select which voltage goes to the PWR pin on the port connection, so the centre pin is the link to the PWR pin. One end will connect to the 3.3v output of the DC-DC converter, the other end connects to (or used to before you cut the track) the battery +ve and the DC-DC input. That's where you want to connect the switched side of your power switch.
Just be careful when cutting the track that you don't chop the link between SJ1 and the DC converter!
Here's a picture I drew earlier :-)
- Derivative work, all right of the original "artist" acknowledged ;-)
Be careful how you connect to the SJ1 pad, as it's only a surface pad, and not a through-hole, it could be easy to overheat it, or expose it to too much physical stress from the wire and pull it off the board! (You don't want to do that). I would recommend routing the switched wire through one of the holes in the AA board and tying a knot so that any strain is taken there, not at the SJ1 pad.