Honestly don't think it'd be worth it. Much of the reason Vali performs as it does, is that it's been finely tuned to the specific curve, optimum linear range, optimal power requirements and I suspect components in the hybrid part of the circuit where probably chosen for their synergy with this tube. I love to 'roll' myself, but really - it should be saved for amps designed for it.
Also there isn't too much at those heater voltages that are worth rolling! It is the ultimate non rolling amp, what you have is what you get. Rather good in my book :)