Would it be possible to add the finesharp plug-in? From what I see there only exists AVISynth code for this. Perhaps a method to add custom AVISynth scripting to the filter chain?
You can use AVISynth with Avidemux but not as part of a filter chain created with the inbuilt filters.
Have to use avsproxy and also tell avidemux to get the frames at the "avisynth port" .
If you have code writing experience:
You would need to write/translate the code to match avidemux filters
along these lines: Writing your own filter (http://www.avidemux.org/admWiki/doku.php?id=tutorial:writing_your_own_filter)