Under certain weather conditions I believe FCO TWR has always had the option of clearing you to take off while the previous traffic is still rolling, with the caution "maintain previous traffic in sight". As I recall it is used especially when northbound departures are alternated with southbound departures, especially when there is a queue forming for takeoff on 25.
Not sure if it is ICAO "approved"? Having said that every county has its regional variations from ICAO, including US, UK and France.
MD