Hm… not really straight forward to do at all.
Let’s turn the question around: What do you want to achieve? What is your end goal? Why the ring shaped pad?
I ask, as you might not really need a ring shaped pad and something else that does appear similar on the finished pcb will do the job just fine…
Did this for an ultra low profile push switch from Snaptron.
Draw a ring in silkscreen, with a thick trace then edit the properties to the appropriat copper layer. Accept the warning and then place an SMT or through-hole pad in the ring, to allow traces to connect.
I get the workaround using the silk layer to make the ring and then changing the active layer to move it to the copper. But note the stencil apertures. I’m thinking that the only way to do this is to follow the same workaround and make the four arcs for the stencil in the silk layer and then move it to the paste layer. Is that the only way to make this kind of arbitrary pad and stenci?
If you run a current nightly (or with kicad 5 which will be released within the next few days if we are lucky) you can use kicad stepup to create such a pad including the paste pads.
(The current Stepup converts circular features to polygon pads)