Hijack has no such file describing the menu items. The menu items in the menu (restore visuals, calculator, screen blanker, etc.) are all hard-coded, though I believe there are config.ini options to hide them if you don't want them.

User apps are inserted into the menu by programatically "binding" to the menu. This means that in most instances, if there's an entry in the hijack menu for a program (empacman for instance) that means it's running in the background.

However, a program called launcher (do a search) has been written to handle this situation more elegantly. Launcher has a configurable file which lists your apps and how you want them started. It also requires another add-on called preinit which starts the launcher itself.

After setting preinit and launcher up properly (they're not easy for novice users, just to warn you) you should be able to have empacman available in the hijack menu whenever you want to play, which is I think what you're looking for.