Используйте сокращенный URI данных в стиле ячейки с формой изображения, например.
graph.insertVertex(parent, null, '', 20, 20, 80, 80,
'shape=image;image=data:image/svg+xml,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;');
Вы можете использовать этот инструмент для кодирования файла SVG.