Air sealing between joists and plaster

Is there a simple way to air seal the plaster joint around a ceiling/floor joist that protrudes out from a straw clay wall? With wood in the same plane as the wall, you can put an air fin behind the wood and plaster over that. All I can think of for protruding wood is to nail and caulk small strips around the board where it penetrates the wall, then attach some kind of air fin to those strips. Anything better?