Coming from a Drupal shop to now working with Kentico more, Drupal Blocks (that do exactly what you are asking) are one of the things I miss the most.
I have thought about replicating them with Kentico by making a "Block" doc type and placing them all in a dedicated folder in the tree and referencing them as necessary. Similar to the solution you posted in the previous post, but with more documents with less fields. I would think this would simplify transformations as you'd really only need one to display any given "Block".