Rename the existing as-install/bin/asant script to asant.bak.
Copy the asant.template file in as-install/lib/install/templates/ee (for SE/EE version) to the as-install/bin/ directory and rename the file asant.
Edit the newly copied as-install/bin/asant script, replacing the %CONFIG_HOME% token with as-install/config.
If there were any manual changes made to the original asant.bak file, merge them into the new asant script.