stdout to stdin pipe using launch-prefix?

edit

I'd like to use launch-prefix to pipe the stdout of a program (netcat) to the stdin of a ros node.

It works fine when launched from rosrun:

netcat 10.0.0.10 8001 | rosrun foo stdin_to_msg.py

I can also copy the command line that roslaunch generates (determined by ps -aux | grep stdin_to_msg.py) and run that successfully, but when run in the launch file the stdout from netcat is sent to the stdout of the roslaunch terminal if output="screen" (or nowhere if not, or a log file?), and the node itself never starts.

<node name="stdin_to_msg" pkg="foo" type="stdin_to_msg.py"
    launch-prefix="netcat 10.0.0.10 8001 |" output="screen"/>

Probably I can wrap this in a bash script and run that from roslaunch, but I'm curious if there is an in-launch solution.