Swanny, no poking involved! - sew a small loop in each of the 4 corners inside the cover, sufficiently big enough to wangle a treasury tag end through & hold in position. Sew one side of a treasury tag onto each corner of the duvet. When you put the duvet in you slide the free end of each treasury tag through each loop in the cover top, wiggle the rest of the cover down & secure tags at bottom corners. Treasury tags used to have metalled ends, now you can get them plastic so it doesn't matter washingwise whether you "tag" the duvet or the cover.
Having gone into this rigmarole, the use of treasury tags was how I first heard it described many years ago, but I'm sure buttons would work fine as well.
Changing duvet covers ought to be an Olympic sport, there are so many variations on a theme; turning the cover inside out before you start replacing it (or not), doing the job at the side or bottom of the bed, involving a "beautiful assistant" who can do it quicker/better/without such huffin' & puffin', optional arguments....
So is it just me who's heard about this method of taming wanderlust in duvets then?
Probably......