If you really want to pass the target-rowspan through a tag, maybe you could pass it through something valid where it won't do anything, like 'align' or maybe 'href' or something?
Bah, wasn't calculating properly so I did need to use another attribute to pass it through with.
Also, firefox requires display='table-row', but IE requires display='block', so I've got to do a browser if thing. :@
Other than that, it's all working... hopefully it stays like that when I plug all these changes back into the original code.