How do I specify a revision for "git blame" by date?

[perryh@xxxxxxxxxxxxxx]

How do I get "git blame" to operate "as of" a particular date in
the past, without having to manually look up the corresponding
SHA1 using "git rev-list"?  For example, I can get a report as of
2011-12-29 by doing something like:

  $ git rev-list --all --date-order --format="%h %ai" .
  ...
  7c69106 2012-01-03 ...
  b4227af 2011-12-27 ...
  ...

  $ git blame <file> b4227af

but I want to have git look up the last revision prior to the given
date, by doing something like

  $ git blame <file> @{2011-12-29}

This does not work as written:  it ignores the date parameter with
a warning:

  warning: Log for '' only goes back to Thu, 10 May 2012 08:14:16 -0700.

If I use HEAD@ instead of just @ I get the same message with 'HEAD'
in place of '', and everything else I've tried gives a "fatal: bad
revision" message.

Clearly, as shown by git rev-list, the log for the _repository_
goes back farther than May 10, so this is a problem of finding the
correct syntax rather than of wanting to do something "impossible".
What do I need to put in front of the @ to cause the entire log to
be examined?
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