Is there a way to customize or change the thumbnailer used in Dolphin?

For mp4 & mkv files Dolphin displays a frame from the video as a thumbnail. My movie collection has embedded poster images (i.e. "covert art" or "artwork") which I would like to display instead.

I see Dolphin use KDE ffmpeg thumbnailer, and there is a (non-KDE) fork of ffmpeg thumbnailer (https://github.com/dirkvdb/ffmpegthumbnailer) which I've got working. But how can I point Dolphin to use a custom binary/script?