Do we know if it takes three separate photos or is there some way that it is able to sample the same photo at three different times?
In other words, the simple thing to do would be to take three photos. After each photo you zero the sensor and start over.
An interesting way to do it would be to start integrating the image then at the first interval you read out the information but leave the sensor data intact. Then after the second interval you read it out again and after the third interval you read the final result. This would give you, respectively, underexposed, normal and overexposed. It would happen faster and presumably would not have a registration problem. Neat trick if the hardware allows it.