a peg to hang a matter on
a peg to hang (something) on
Something that functions largely or primarily in service of expressing or presenting something else, often one's opinions, beliefs, or ideas (about something). Because of the persistent (but incorrect) notion that one shouldn't end a sentence in a preposition, some writers prefer the form "a peg on which to hang (something)." It become clear from very early on that the director is using this adaptation as a peg to hang his own political agenda on. The musical is primarily a peg on which to hang a plethora of catchy, upbeat song-and-dance numbers, so most audiences will likely be willing to forgive its laughably thin story.