Has anyone created an add-on package which would allow admins to edit theme files via dashboard? I already know how to add customize-comments to css files so that the styles can be edited in dashboard, but this is rather restricted.

The point is that if an CSS-savvy client would like to add some new lines to style sheet, but would not like to (or is not allowed) to use ftp connection to the server.

Basically it would only need to loop through theme files (css and maybe php) and open them in textareas for editing. If no one has done this before, I might start to do it by myself, but of course I'm looking for a already complete solution if possible.