Good idea, and a good suggestion for my first stab at writing a plugin. I'm not finished yet, but I thought I would throw it out tonight. The idea is that it adds a Themes page. On that page, you can create an new file, upload a file, or delete a file.
Upload is not yet implemented because I have not figured out how to do it yet.
Also, the page is out of date after creating or deleting a file.
These problems are easy to fix, but it's waaay past my bedtime. I'll work on version 0.02 soon.
The plugin is at wp-plugins.net, under Themes, Styles, and Decoration. You can also go straight to my web site: http://tempest-sw.com/wp.