Reading your post gives me the sense that you've never played with plugins to Paint.NET. You might want to download the various plugin packs that are "stickied" in the Plugin forum.
For example:
There is a "feather" plugin in my plugin pack.
You may also like my "Color Balance" effect plugin.
For instructions on how to download and install plugins, look here: http://www.boltbait.com/pdn/InstallingEffects.php
Hope this helps.