Problem with flipping !

Hi all ! I have a problem with the way I flip my characters in order for them to face the other direction. I put some 2D characters in a 3D map, with lightning and all that. At first I imported them in the scene as sprites with the sprite shader set to diffuse. It works, my characters are seen either way. But the sprite diffuse shader is a bit poor in possibilities, and I would like to light my (flat) characters with the standard shader to add normal maps and what not to enhance the light and reflections, even on 2D objects. BUT when I put the standard shader on my sprites they disappear when they flip (backface culling). So I looked up and people advise to modify or write a new shader to override the backface culling but I don't really care about backface culling since my sprites are flat and never the backface and front face are seen together. I'm just curious if there's a simple way to make my characters look to the right or to the left without reworking the shaders and all...