I don't remember the details of how I did this, but this was necessary for a module I published years ago to CPAN, Test::MonitorSites. A review of that code will likely turn up some useful clues.

UPDATE:

OK, this seems to be the code which did the trick:

  my $Test = Test::Builder->new;
  my @handle_names = qw/ output failure_output todo_output /;
  my %old;
  $old{$_} = $Test->$_ for @handle_names;
  $Test->$_(\*STDOUT) for @handle_names;

  # which was restored like so . . . 
  $Test->todo_output(*STDOUT);
  $Test->failure_output(*STDERR);
  $Test->output(*STDOUT);
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-- Hugh