Did you ever find an answer to this? I have the same issue – a village information site (see http://www.stbees.org.uk – currently HTML) with multiple areas, each with its own sub-menu. I’m trying Weaver but that has only 2 menus and those are general ones, not specific to a particular page. I’ve figured out a work around using a Text widget which only appears on single pages and listing the sub-menu items there with links to the sub pages, but that seems clumsy.