Having issue trying to run Island threads in gazebo_ros using roslaunch

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Am trying to simulate multiple robots in my gazebo and do not wish to use Parallel simulations as i wish to test for collisions. https://github.com/alidemir1/RosGazeb...

I wish to input this command

gazebo --verbose -o split_unthrottled2 \

mentioned in http://gazebosim.org/tutorials?tut=pa... and place them inside my roslaunch file.

<include file="$(find gazebo_ros)/launch/empty_world.launch">
<arg name="paused" default="false"/>
    <arg name="use_sim_time" default="true"/>
    <arg name="gui" default="true"/>
    <arg name="headless" default="false"/>
    <arg name="debug" default="false"/>
    <arg name="verbose" default="true"/>
    <arg name="world_name" default="$(find multi_robot_test)/worlds/test.world"/>

</include>

How can i place this (-o split_unthrottled2 \ ) to perform my functionality?