Thank you very much @jacklul
Based on your git repo: https://github.com/jacklul/asuswrt-scripts/tree/master/asusware-usb-mount-script, I finally manage to overcome my ISP limitation.
cat > /tmp/installer.sh << 'SCRIPT_EOF'
#!/bin/sh
# --- COLOR SETTINGS ---
C_RESET='\033[0m'...