Not sure if I understand what you are going for? BTW, I think that looks great and the pool guy can find the skimmer. Make it square like a paver, and he is going to charge overtime for finding the skimmer every trip.
Is the skimmer port not round all the way to the top and designed only for a round lid? I guess if its not flush (like my round one), you could just use a paver with an aluminum or stainless back plate on it. This suggestion would work for those type skimmer lids that go down into wood decks and protrude down and are not flush. If yours is that way, who needs a lid under the paver?
I know Hayward used to make square lids as my older pool has one. The skimmer is round and comes up a round tube, but when it gets two inches from the top, it flares out from round into a square that is just slightly larger then the tube diameter. The lid is flat and fits into the square recess.