I can't think of any simple way of doing this within Radarbox.
You should be able to write an SQL query that looks for EGKK at the start or end of the flight route in the MyLog database.
SELECT DISTINCT
Flights.Route,
Flights.Callsign,
Flights.EndTime,
Flights.ModeS,
Flights.MsgCount,
Flights.Registration,
Flights.Session,
Flights.StartTime,
Flights.StartPosition,
Flights.EndPosition,
Flights.StartAltitude,
Flights.EndAltitude,
Flights.StartGS,
Flights.EndGS
FROM
Flights
WHERE
(Flights.Route LIKE "%EGKK%")