It is not possible, DVR stands for Digital Video Recorder, in the case of your old setup box, it is simply an additional disk of memory with the receiver to save the video footage being received by it from the satellite, normally the EchoStar 110 satellite. For a security camera system, the recorder itself would need to not only accept the video feeds but decompress them and display them, then store them. A complete redesign of the Mother Board would be required. 

I strongly suggest just to purchase a Security Camera Recorder either an NVR or a DVR. Give us a call at 866 573-8878 option 2, to speak to a Sales Expert and guide you to the correct components for your location.