[development] Change menu structure at runtime

Hi, I want to do a "strange" thing with the (Drupal 6) menu system. After defining a menu structure, let's assume that it is a "primary navigation", when viewing a node page I want that page to be under a specific menu item in the menu "primary links". See this: - primary navigation -- menu 1 -- menu 2 -- menu 3 ---- node/80 (this will be changed at runtime) That "node/80" path will be the child of a menu item, according to some conditionals that I have in hook_nodeapi. So the question is: can I alter the menu structure at runtime, while not changing database or persisting those changes? Or perhaps there is another solution... Thanks, Fernando