I asked this a year or so ago for my purposes, but now I have a friend in the same situation, and I believe the answer is the same:

He has another friend who is a GS who said he will sponsor him on a gpu upgrade on a mileage award ticket. I said it's not possible UNLESS the miles came from the GS account (how it was last time I asked). This is still the case, right? For clarity - my friend X used his non-GS miles for a ticket, and now his friend, Y, said he would sponsor a GS GPU since GS can upgrade award tickets. This still can't be done and has not changed, right?