How to make sure that two nodes (rosbag/record) start at the exact same time?

edit

I have a setup consisting of two computers as described in my previous question. I want to synchronously record rosbags on those computers. Therefore I am using a launch file, that looks like this:

<launch>
    <machine name="comp2" address="10.0.0.1" user="user" env-loader="/home/user/catkin_ws/devel/remote_env_load.bash" default="false" />
    <node pkg="rosbag" type="record" name="record_kinect" machine="comp2" respawn="false" output="screen" args="--duration=5 -O /home/user/test.bag /topic3 /topic4" />
    <node pkg="rosbag" type="record" name="record_atis" respawn="false" output="screen" args="--duration=5 -O /home/user/test.bag /topic1 /topic2" />
</launch>

Later on I'm planning to use the python script that is referenced here to merge those two rosbags. However, it would be a great advantage and simplify my work, if there was a way to make sure, that rosbag starts recording at the exact same time on both machines. Is there a way, to tell a node in a launchfile to wait for another node or something like that?