not without reimplementing it

> and now it looks:

my %matches = %+;
sub(\%matches);
[download]

why not just

func( { %+ } );

this will pass the hashref of a flat copy, without messing with the globally tied %+

update

demo in debugger

  DB<18> use Data::Dumper

  DB<19> sub func { say Dumper \@_}

  DB<20> 'ABC' =~ /(?<a>\w)(?<b>\w)(?<c>\w)/; func({%+})
$VAR1 = [
          {
            'a' => 'A',
            'b' => 'B',
            'c' => 'C'
          }
        ];
[download]

NB: if you are only passing the named captures, why not just flattening %+ to a list?

  DB<22> sub func { my %matches = @_; say Dumper \%matches}

  DB<23> 'ABC' =~ /(?<a>\w)(?<b>\w)(?<c>\w)/; func(%+)
$VAR1 = {
          'a' => 'A',
          'b' => 'B',
          'c' => 'C'
        };
[download]

edit

s/sub/func/ , since sub is a keyword