Ok, so here is how I do it (there may be an easier way I don't know). Select your mesh and go into edit mode and go into face selection instead of vertex selection [Fig1].
Make sure you're on the editing tab [Fig 2]
Open up the Texture Face box if you don't have it open already [Fig3].
Select one of the faces on the mesh you want to have double sided textures, then click the "Two Side" button under the Texture Face options [Fig 4]
Select all the other faces (hit A for all select) then press the copy button [Fig 5]
On meshes where you only need a few areas as double sided textures you can select the needed faces by hand instead of selecting all.