Living in the land of three-hole duvets, we do have one children's duvet cover that only has the bottom hole.

It's not that much harder. My process is flipping it inside out, then sticking your hands in and gathering the fabric on my arms until I get to the far end. At that point grab the duvet through the corners, lift and shake to straighten.

Obviously it helps that it's kiddie size and I'm just shy of 2 m, but it's not that different from the three-hole "put hands through holes, grab duvet and shake".