Seem like another instance of impossible folding devices (see mass effect for other examples). Still, you could do somethings that would get you a "folding" shield. However, the unfolded version would most likely not look smooth or hold up to any kind of pressure. The first idea that came to mind was a telescoping type system; however, this means that the unfolded shield would have clear ridges where each layer overlapped. There is also the issue of constructing such a design, which would require more percision than may be easily possible (not sure on budget or your resources).