Adinoto,
a weight with a hole in the center , is the way to do it. I had the same clamp and returned it for the same reason.
Since I'm using an after market counterweight, the stock weight works great as a clamp . It's not too heavy and effective.
I stuck a rubber sticker pad , the same circumference as the weight and made a hole in the center. You could also use felt. This is slightly heavier than the weight ,but around the same size as the one on my SCD777.
I do notice slightly better focus with some records. And it does a good job flattening.