How to remove an specific href from a top-menu link in magento?

Question

I have an specific cateogry (top-level / main category) witch shows a menu on hover at menu. I need to remove the href from that < li> item, or replace href value for "javascript:void(0);".

I'm trying to do this with page_block_html_topmenu_gethtml_before and page_block_html_topmenu_gethtml_after observers, but didn't get it yet.

I wouln't like to make a replace in block's html output. I don't think it's a good idea. =O

Does anyone have any idea?