Hide all files with a specific extension from Finder

I have an application that creates MANY .log, .upload, and .json files each day, so that when I go to my "Today" smart folder, it's all clogged up with those. I'd like to hide all three of those file extensions from finder, but I'm not sure the best way to do so given that I'd need the solution to work on new files with those extensions as well as existing ones.

Alternately, I could hide all existing and new files in a particular folder since that folder houses all of those, but I want them also to be invisible to my smart folders.

Thanks for any help you can provide. I'm confortable USING scripts and automator and such, but I don't know the commands myself, so the more specific you can be in your answers, the better.

Thanks!

If you just want to modify the saved search, copy it somewhere from /System/Library/CoreServices/Finder.app/Contents/Resources/CannedSearches/Today.cannedSearch, show package contents and open search.savedSearch in a text editor, and add this to the first RawQuery key:

&& kMDItemFSName != *.log && kMDItemFSName != *.upload && kMDItemFSName != *.json

You can drop it on the sidebar by holding command.