Last few trips, including a few weeks ago they were sending all the SB to the left, and LL to the right. I would think if LL got slow they would send some over but we never saw that. I'm sure if you go in LL you can ask for left.
But as with lots of attractions like this, operations change all the time but my guess is if you go in LL you can request. If you go SB and you see them sending both ways I would ask as well.