In Commercial Districts, for zoning lots or portions thereof, with street lines along the elevated rail structure on Jerome or River Avenues and within 100 feet of such street lines, the permitted obstructions set forth in Section 33-23 (Permitted Obstructions in Required Yards or Rear Yard Equivalents) shall be modified to permit any building or portion of a building used for any permitted use other than residences, to be a permitted obstruction within a required yard, rear yard equivalent or other open space required pursuant to the provisions of Section 33-20 (YARD REGULATIONS), inclusive, or Section 33-30 (OTHER SPECIAL PROVISIONS FOR REAR YARDS), inclusive, provided that the height of such portion of a building shall not exceed two stories, excluding basement, nor in any event 30 feet above curb level. Any allowance for other permitted obstructions above a building in a rear yard or rear yard equivalent set forth in Section 33-23, shall be permitted above such modified height limitations.