I would like to suggest that there should be a way with which i can prefix image paths in editor only (not present in the return of a getContent() call). Consider the following directory structure:
web/ editor/ index.php images/ image.jpg index.php content.html
The main index.php brings up the contents of the content.html which is edited by TinyMCE working in editor/index.php. Now image paths should be like images/image.jpg when presenting and should be ../images/image.jpg in the editor. This could be achieved conveniently using an editor property.