It's physically possible but not easy because individual 16T cogs are all but impossible to get. Several years ago I made a couple of 13x27 9-speed cassettes by substituting a 13T first position cog for both the 12 and 13T stock cogs and adding a loose 16T cog and spacer.

However, I had a lot of trouble locating the 16T single cogs at the time and, for all practical purposes, they aren't available in either 8 or 9-speed form (both would work but you can't find either) by now.