a switched set up wouldn't be hard, RB VCT solenoid and inlet actuator, tee the oil pressure sensor for oil feed, rpm activated switch. Hardest part would be blocking the oil feed for the front cam journal and routing and drilling for the solenoid in its place. You would want a TIG on hand just in case you drill in the wrong spot!
continual variable would be a challenge, since you need to add cam position sensors, a better solenoid (PWM), actuator and an ecu that not only has target cam position, but that can actually control it and do so within 10ths of a second