Unfortunately, this is not possible to do. The encryption is there in order to prevent you from seeing what is inside the model, but we would need to see what is inside in order to do an import.
The only way that I'm aware of to achieve such a result would be to do co-simulation, where a SPICE tool is used to simulate the encrypted models and then this is connected to Simulink. As far as I am aware, PSPICE and Simulink can work in this co-simulation mode but you would need to contact OrCAD for details. I'm not aware of any similar capability for LTSpice.