Using pypy with ROS for better performance ?

edit

How can I use pypy instead of the default python interpreter for a ROS node written in python ? I tried:

cd /path/to/node
pypy script/pioneer.py

But I'm getting an error:

Traceback (most recent call last):
  File "app_main.py", line 51, in run_toplevel
  File "scripts/pioneer.py", line 5, in <module>
    import roslib
  File "/opt/ros/groovy/lib/python2.7/dist-packages/roslib/__init__.py", line 50, in <module>
    from roslib.launcher import load_manifest
  File "/opt/ros/groovy/lib/python2.7/dist-packages/roslib/launcher.py", line 42, in <module>
    import rospkg
ImportError: No module named rospkg

Also, changing the first line of the script to #!/usr/bin/pypy and using rosrun yields the same.

EDIT: OK, I added the missing directories to sys.path (namely /usr/lib/pymodules/python2.7) but now I'm getting another error:

ImportError: No module named _tf