As I use mylog reporter solely for the purpose of producing logs on the mode S yahoo group. I am not interested in routing history being stored in mylog. I post to Yahoo purely to take advantage of the Parser service and to show aircraft that were airborne on that day, rather than to be completely accurate will all flights tracked for specific aircraft over a day.
What I do before asking for the reporter log is to look what time that I recieved the very first aircraft on the day in question, then I set the 'delete old data' tab to a time 20 mins before this. This deletes the flight details for previous days without removing the aircraft record or todays flights from my logs. Of course it means in the log it only shows the first flight you track for that aircraft on the day in question, but it means that you are not displaying historic routes flown on previous days in your reporter.