If you want to stop the tour until the user specifies the start, you can add in the pause tag:
<gx:TourControl>
<gx:playMode>pause</gx:playMode>
</gx:TourControl>
There are no variables in the tag to change, it will simply pause the tour until prompted to restart by pressing play on the tour controls:
Tour controls
...
<gx:FlyTo>
<gx:duration>5</gx:duration>
<LookAt>
(truncated to save space)
</LookAt>
</gx:FlyTo>
<gx:TourControl>
<gx:playMode>pause</gx:playMode>
</gx:TourControl>
<gx:FlyTo>
<gx:duration>5</gx:duration>
<LookAt>
(truncated to save space)
</LookAt>
</gx:FlyTo>
...