Which model is yours? Mine is a PA70ES.

I just double checked the firmware setup and it seems I was misremembering things. There's a toggle between "DISCRETE" and "MSHybrid" which means dGPU only and hybrid iGPU + dGPU graphics. I use it in MSHybrid mode with nouveau drivers. This keeps the dGPU in the lowest possible power mode.

It still wastes around 7-15 W doing pretty much nothing according to my monitoring script. That's the entire power budget of a single board computer like the Latte Panda Mu.