Recently I had to machine a few pieces after turning.
Because the very top of the part was supposed to be machined off, I could not clamp through the central hole like I often do.
Decided to quickly turn an expandable washer out of aluminum and a plastic spacer that would collapse a little bit under clamping pressure and allow the part to sit firmly against the base of the fixture.
I liked this method so much I am going to do the same next time I have similar part to make.
See pics below.
Later on i will try to post some more pictures of other setups I did.