I've managed to discover a bit of a workaround. It's not perfect but it actually lead to better results than I was originally hoping for. Funnily enough you can get any of your companions to choose to become divine if you just have another player join you and take control of that companion and only that companion and then have them choose to take the power of divintiy for themselves.
In essence, it changes absolutely nothing for "Purge the wolrd of source" and "Give source to the people" endings however...
I chose Fane to become Divine as I originally intended and most of the game proceeds as though you were the new divine which means that a lot of people are quite quite happy with the outcome even though the war against the war is still raging on. Moreover according to Fane himself his people, the eternals are back and even though you can confront him about enslaving your people, the epilogue slides mention nothing of the sort. And while this is clearly a bug I quite enjoy this outcome ragardless.
