After 4-5 different pillow setups (including child flotation pillows and the inflatables sold at BPL), I've finally settled on one that works for me. It's the most comfortable UL setup I've found, and it adds 0.0oz to my setup.
I take my 500ci stuffsack (homemade version of the ones sold at BPL), and insert my folded pair of rain pants (folding them in half and then in thirds creates a nice, smooth rectangle six layers thick). Then I add my 4L Big Zip platypus. On top of this I add my rain jacket. I then take one deep breath and inflate the platypus. I am able to put the cap on fast enough that it traps most of the air inside. In fact, most of the time it automatically deflates to the perfect thickness. Finally, I loop the draw cord around the platypus cap, keeping the stuff sack secured onto everything (it doesn't all fit into the sack completely; some hangs out the opening, but it all stays together with the drawstring over the cap).
Since I never go to sleep in my rain gear, I will always have these as a pillow option. And serving this dual function helps me justify the added weight of a rain suit (something I am inclined to bring anyway in the PNW). The stuff sack keeps everything together and keeps my head oils away from the waterproof-breathable membrane. The stuffsack will also keep wet rain gear isolated from my sleeping environment.
The trick I found was to stow the rain gear in flat layers rather than rolling the rain gear around the platypus. I've found that this creates a much more level surface, and I don't notice any "bubble" effect (that is, it doesn't feel like my head will roll off the pillow or that it will slide out from underneath my head). This is in part due to the larger 4L platypus and leaving it partially uninflated. But I also think that by folding the clothing rather than rolling it, the edges are thicker (due to the fabric folds), adding stability to the platypus. Also, it is much easier to fill the stuff sack with empty layers than to roll everything up and try to squeeze it in.
I carry a 4L platy anyway so that I can take warm showers and camp away from water. But most of the time my 2L wide mouth bottle (my on-the-trail water bottle), holds enough for camp, thus freeing the Big Zip for my pillow. So the Big Zip platy serves 3 functions: extra/backup water storage, pillow, and shower. That alot of functionalith for 2.3oz, and worth the extra tenths of an ounce over the 2L version. Therefore my net weight for the pillow is 0.0oz, and every component is multi-use.