If you buy MB Looks it comes with the standalone Look Builder application which can be used on stills. It doesn't function within PS, but taking more of the film color/grading workflow, you can do your touch-ups, cloning, etc in PS then move to Looks Builder for import/grade/export. I don't know how extensive it's import/export ability is though.
I imported a .jpg right off my D40 (6mp), messed with it, then exported back to jpeg. I think it exports back to jpeg if the import was a jpeg, and it will export to a tiff if the import was a tiff. I don't think there is a frame size limit.