Yes, 'echo 1' will work.  It's a shell built-in but seems to do the trick.

Echoing "1" is potentially confusing because SuperSu treats the "1" as a UID:

    razr:  adb shell su -c 'echo 1' --> "1"
    xoom:  adb shell su -c 'echo 1' --> "su: exec failed for echo 1 Error:No such file or directory"

    razr:  adb shell su -c echo 1   --> ""
    xoom:  adb shell su -c echo 1   --> "su: exec failed for echo Error:No such file or directory"

So, instead of "1", I'll use "x":

    razr:  adb shell su -c 'echo x' --> "x"
    xoom:  adb shell su -c 'echo x' --> "su: exec failed for echo x Error:No such file or directory"

    razr:  adb shell su -c echo x   --> "Unknown id: x"
    xoom:  adb shell su -c echo x   --> "su: exec failed for echo Error:No such file or directory"