- Shadow the feed with Feedburner.
- Enable the Convert Format Burner, and convert your feed to RSS 2.0.
- Use Yahoo Pipes to filter the feed (because Feedrinse seems to be broken).
This let me create a feed that excluded all my posts containing the fbpost tag, thus allowing me to avoid yet another postgasm in Facebook when adding new import URL to notes.
While fiddling with this I came across this article that discusses a number of tools (some no longer available) for processing RSS feeds.