I always laugh when this question is posted since people think Disney "invented" single riders lines (which, of course, isn't true) - and they still only offer it at one ride.
Anyways, even with Universal Express, the following attractions offer single rider lines:
Men In Black
JP River Adventure
Ripsaw Falls (offers Doubles line)
Note: Singles lines are typically not opened unless the stand-by line is 30 minutes or more.