Yes, Petal is another possibility. The only problem is that it embeds the commands in tag's attributes, so it is still well formed XML but I can't edit the commands from within OO editor. :(

This requires the person creating the template to open the ODT file, extract the XML part, edit it and repack... This procedure is certainly possible but requires an operator much more skilled than the ones for which my project is designed. And this is why I decided to avoid LaTeX that would be the obvious choice if only I could redesign the brains of my users