Yep, this is why many people running WVO will use a dual fuel setup with real diesel for start-up. The injector head has a very good thermal connection to the engine block. If it is cold, the injector is going to be cold. It would take some major surgery to isolate the injector head and when the engine came up to temperature, you'd sure miss all that free heat for your fuel. Maybe use a heat pipe? for it's thermal diode effect? Too complicated.