How to apply 2 sides render in BGE v2.5

Hi all,

I’m new and I never used Forums before and I start using Blender one month ago.
I have a problem, I want to render the polygons of this mesh on both sides with the BGE, so I selected all the faces (with A) in edit mode and, in the object data tab, I checked the two-side option but it works only with the last face selected. I’m sure there is a way to apply the option to all the faces selected.
Probably is a very noob question but still…

Thanks in advice!