these are 700cx25mm *used* road tires going onto brand new Chinese rims.
If nobody suggested this yet - buy chinese tires for those rims.
As an aside, I once had a Ford van rear door glass pushed in by thieves, found it laying inside the van with the rubber lining that it is normally seated in. I was very much puzzled how to put it back, basically if you don't know the trick, you are well stuck. I went to this auto shop where they showed me the trick, took just a minute to pop it in. I am sure everybody knows the trick, won't bother to describe it.
However it is not something you could do on the road unless you were prepared to do it. For the bike it would only solve the initial putting the tire on, then you'd have to hope that the tire would stretch a bit to fit on the rim easier next time, like on the road.
BTW speaking of the impossibility of fixing a flat on the road with this tire rim combination - I once had new tires put on the van in an auto shop and one day, luckily it wasn't by the road side, I needed to remove the wheel and found I couldn't do it with the standard tire wrench. And in those days, I was young and in full strength, although no brute to be sure. Those impact wrenches they use in car shops virtually veld the nuts on and without it, it is near impossible to undo those lug nuts. Meaning if I got a flat on the road, I wouldn't be able to change to spare wheel, similar situation to this predicament here.
As to sanding the rims, I suspect that rim walls are not solid material inside, but are bent 180 degrees back at the very edge of the rim, so the brake surface is actually an outer wall of the rim side, meaning that if you sanded off the thickness of the folded material right in the place where it is bent backwards, the rim would just fall apart?