If you're not using the "Recognition Global Hotkey" option on the "Hotkeys" tab of the VoiceAttack options window, you could set that to either "VoiceAttack listens while keys are down" or "Listen then stop listening after recognition completes"
(if you have no intention of using an actual hotkey, you could set that to something you're extremely unlikely to press, like left Shift right Ctrl left Win right Alt Scroll Lock)
Otherwise, if you either only use one profile, or have a specific profile load on startup, and that profile is editable, you could either create a command and assign it to the "Execute a command each time this profile is loaded" profile-level option, or edit the command currently assigned to that option, and add the "Make VoiceAttack Stop Listening" action to it.
If you use multiple profiles, you'd need to configure each of them with such a command/action.