It doesn't appear that wipe R2L is an available transition. Your only option
if you must have that would be to;
1) cut enough off the end of the 1st clip and enough off the beginning of
the second clip to fit the wipe L2R transition. Place the cut clips in the
timeline (clip1 clip2) with the wipe L2R transition. Then put a rotate 180'
"effect" on both clips. Save this "movie". Then put this saved movie in the
timeline and put a rotate 180' effect on it and you'll have your wipe R2L.
2) Do the same as above without cutting the clips.
Remember, don't change the order, just apply the rotate 180' effect.
NOTEKY