This is a simple Python2 script to make use of Sonoff without flashing firmware. Tornado is needed in order to run it. Install it via sudo pip install tornado. All the following is done in an RPi.
Fill in the variables in init.sh. Fill in the IP for your RPi, and pick a port for it.
Long-press the button on Sonoff so that the LED flashes fast. Sonoff will create a new WiFi hotspot. Connect to it (password is 12345678). Then run init.sh. You will get the deviceid in the output. With the deviceid obtained, fill in the variables of sonoff-server.py.
Run sonoff-server.py. Your sonoff should be set up in around 10 seconds. After that, do a GET request to https://IP:port/command_on or https://IP:port/command_off. You may run it using a browser or just curl (e.g., curl -k https://IP:port/command_on).