There is a registry entry to modify for you
http://www.msgplus.net/help_registry.php :
Key: HKCU\Software\Patchou\MsgPlus2\your@email.com\Preferences -> AutoAwayAlways
Value: 1
Description: Boolean value. If false (0), the "change status after x minutes" feature changes the status only when the user is currently Online or Idle.