Slide cube map over car

Because they are recorded from a fixed point, there is no simple way to move the origin of a cube map. If this is for a racing game, you are probably better off looking into screen space reflections:

http://u3d.as/content/livenda/candela-ssrr-advanced-screen-space-glossy-reflections/6Ty

http://u3d.as/content/bruno-rime/hard-surface-shaders-pro/1Rv

 

On mobile, you'll be much better off rendering to a texture to do reflections (whether those are in screen space or using another camera angle).