Menu Assignment

Are there any plugins that allow me to assign a particular Menu to a Post or Page within the WordPress UI, rather than having to do this in the templates?

If not, I need to build this myself. Do you think it makes sense to simply create a plugin that (a) creates a custom field asking for Menu name, and (b) the template calls this field and if not empty, it pulls the menu of that menu name in.

It’s for sub-navigation, for those curious.

Ideally, there’d be a plugin that did what Widget Logic, but for Menus. But since that’s far beyond what I can code, is this a good route for me to take? Any ideas appreciated.

I’m on WP3.0 beta.