I found the bulk import option easily, but I can seem to find the how to add posts individually to a pool. Am I just blind, or is there something I'm missing?
The easiest way you can add a Single image is searching for it by id. You can find the ID in the Statistics block of the image's page, and the URL, whichever you find easier.
Type id:(insert id number here) into the bar. It will give you only that image.