2 people private session, any track (preferably one of those short Ovals), 1 lap race.
The servers reset time is 1 hour so after starting a match you can just sit on a starting line for about 55 min.
No rubber band is needed, your wireless pad may go off, it doesn't matter.
Just be sure to finish one lap and end the match before the clock hits 60 min.
Go back to lobby and start next race.
Only one person need to finish a race and the time for another person will count too.
After joinig a session your friend can actually do nothing.
When you finish the race the game will automatically boot him back to the lobby and you can start next race by yourself.
Another thing i found is that after you start a race and the other person leave, the game will not end the match.
You can sit there for almost one hour by yourself than finish the race and the time will count.
It may be useful when only one person need the achievement.