Preset groups or "sub-presets" for imagefield display formatters

I currently have three presets for an imagefield on one of my sites: main content, teaser, and thumbnail. I'd like to be able to have "sub-presets"--say, an alternate thumbnail that's processed mostly the same way, but aligned with the top of the image rather than the center. The main thumbnail preset would be used by default everywhere the thumbnail format was used. However, if the normal thumbnail preset wasn't quite right, I'd like to allow the user to specify on a per-image basis that a different "sub-preset" should be used, and then that "sub-preset" would replace the default everywhere my thumbnail appeared.

Is this possible?