Can I run aluminum backed organic brake pads with Elixir Avid 5 hydraulic system?
Yes, there are aluminum backed organic brake pads available for the Elixir series brakes.

The SRAM part number is 11.5015.040.020 with the description [Disc Brake Pads Organic/Aluminum - Elixir 20 sets], according to the 2014 SRAM Spare Parts Catalog.