There appears to be a scalar to control the speed of the pixel output clock. If the main clock was borrowed from an Arduino's 16Mhz one, you could get the pixels to fall out as slow as 250Khz. You could possibly read them in at that rate -- just.
There is not going to be enough memory to hold anything like a whole frame in RAM. And writing to the SD is not fast enough to keep up with the 250KHz clock rate of data coming out of the camera.
So what you would have to do is read the image in pieces. Wait for a frame boundary, count through the bytes to some preset point, read the next chunk of bytes into RAM -- maybe 512 bytes or a K, then discard the rest. Append the bytes to the SD file, go back and start over. You will wind up with a frame saved on the SD that is assembled out of multiple input frames.
It won't be easy.