There's a possibility to add additional help sources in IDLE via

    Options -> Configure IDLE... -> General -> Additional Help Sources

Use case:

> If someone wants to download certain version of Python documentation in HTML and specify local "index.html" to be opened by custom menu item which appears the in Help menu.

Problem:

> It's not possible to assign custom hot-key (Options -> Configure IDLE... -> Keys) for such menu items or reassign <F1> to that new menu-item, which actually makes sense when talking in context of the use case specified above.

This use case was taken from real life (stackoverflow site):

http://stackoverflow.com/questions/12174255/linking-offline-documentation-to-idle-linux