How can I dynamically add a sub menu based on a database value?

I have a sub menu that should only be displayed to a few users of my site. There is a menu called Team Calendar with several sub menus pointing to various pages. I need to add an additional sub menu only for these users. I know membership can generally do this but the way we are using it, it cannot. I need to be able to do this with code by checking the value of xxx_is_admin in table xx_usermeta. If the value is "Yes" then the sub menu should be displayed, otherwise it should not.