My knowledge of SVG editing tools is limited, but one option I'm familiar with is svg-edit. While it may not be as robust or advanced as editors like CKEditor, TinyMCE, or FCKEditor, it serves its purpose. Implementation may not be as straightforward due to its script-like nature, and customization may pose some challenges.
It's unlikely that you'll find something with more convenience, but it's worth giving svg-edit a try. You can access it here or here (please note that it may not work on Internet Explorer unless you have Chrome Frame installed).
If you do decide to test it out, I'd love to hear how well it aligns with your needs!