Can be added, but you would have to change a lot of parts for it, like change ECU for starters that should come with a matching set of keys, then add wiring for the RFID antenna in the dashboard, the odo meter would need to be changed if it doesn't have the indicator for the immobiliser.
Its very much possible if you have a budget big enough, still changing the car to newer model would be recommended to avoid any disappointments.
If anybody is up for the project then why not go all the way, go to the junkyards take chances finding the complete smart entry system with push start.