In this bug that i tried on 3 L2J servers they all worked.
So what you do is the following:
A. You need to get married to the person you want to 2 vs 1 with.
B. One of the two of you sign up for olympiad
C. Once your "significant other" goes into olympiad
D. The person outside olympiad type [glow=red,2,300].gotolove[/glow]
E. Once your in the olympiad and they start match you will be able to hit the opponent or you can even be a healer and heal your friend.
P.S. Im positive this will not work on official and most likelky work on servers that dont know how to fix bugs well...
Heres A Screen Of Some One Doing It To Me:
http://img169.imageshack.us/my.php?image=awamb2ue9.gif
Enjoy