You can reduce the framerate by using a camera and disabling and enabling it over time. Basically, when you disable a camera it "pauses". Follow these steps:
- Create a new camera in the scene.
- Create a new camera texture with your new camera selected (Add New -> From Camera in the Resources Panel).
- Create a script that enables the camera for a single frame. And then, keep doing this over time e.g. 1/10th of a second.