It looks as if the upgrade restrictions are gone and we are now able to do an in-place upgrade even when the Users folder remains on another drive than C:. Please read my post about this in another thread: Windows 10 build 10162 Released - Page 63 - Windows 10 Forums
Anyway, this needs some extensive testing before we can be sure but at least I can say that this laptop I am using to post this had Build 10159 last night, with the Users folder relocated on E: drive. This morning I woke up to an upgraded Build 10162, all my users still intact on E: and absolutely no issues. It looks promising but really, as I said, needs more testing before I am willing to remove the upgrade warnings and workaround from this tutorial.