I can't do that, since my Xeon doesn't have an (activated) iGPU, nor am I willing to buy an AMD card with comparable performance to my GTX980, just because iBooks doesn't work. Instead, I'm using Calibre and Clearview in the meantime. Yes, it's inconvenient, but at least I can read my documents. Luckily, I don't have this rendering issue with any other application.
I'm still surprised how long it takes for Nvidia to fix this. I assume they won't address this issue until 1.12.2 or even 1.12.3 ships. Oh well..
Just to add, FCPX rendering is also broken in the new drivers with Sierra. My BruceX times with a 980ti went from 12s up to 50s. I opened a support ticket with Nvidia and they told me that they did not support this card on a mac pro. They told me to call Apple. I can't tell you how irritating/frustrating that is. Of note, my OpenCL and Cuda scores are still off the chart with this card. It is literally these applications which can't make use of it.