The puck in the jack point is actually crafted to insert into the plastic. I know it might not seem that stable. I thought the exact same thing when I saw someone post a similar picture, but when it was down on the jack stands it was pretty rock solid. I wanted to mount the jack stand the way you were talking about, but the grooves in my jack stands were so deep I was afraid it might run into the car.
WP_20150708_16_07_43_Pro by
jsk945, on Flickr