How can I override .hgrc options on the command line?

I typically want to ignore white spac开发者_Go百科e changes when diff'ing with mercurial. If I set this as a default by putting ignorews = true in my .hgrc's [diff] section then there doesn't seem to be a way to force the display of white space changes for a single invocation on the command line. What am I missing?

FWIW: None of the relevant command line options accepts an argument. Using the (deprecated) [defaults] section has the same behavior. I'm assuming the final answer will be "use an alias for ignoring space", but am hopeful something better exists.

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From the hg(1) man page:

   --config
          set/override config option (use 'section.name=value')