I am not at my Mac, so this is untested but I am pretty sure it can be made to work with minor edits...
Change your script so it looks like this and your python script runs in the background saving its output to a temporary file $$.tmp
where $$
is your process id (pid):
export PATH=${PATH}:/usr/local/bin:/usr/local/CrossPack-AVR/bin
cd /Applications/MyApp
/Applications/MyApp/doIt.py "$1" > $$.tmp &
Now add the following lines at the end, so that you 1) create a script that tails your log file, 2) make it executable and 3) you execute it:
echo "tail -f $$.tmp" > x.command
chmod +x x.command
open x.command
I would recommend renaming x.command
as $$.command
so that you can run it multiple times from multiple users without interactions between the various users. You should also clean up and delete the temporary files after use.