Use "Flex" feature to close an open clamshell model

Can anyone get this to work?

I have a finished model of a clamshell-type PET package. As it is now, it's in a fully open state (as-molded). However, I want to use the "Flex" feature to add a configuration to the model that shows it fully closed (for demonstration purposes).

The model is attached here.

Thanks!

SolidworksParts And Features