How about:

#!/usr/bin/perl

sub foo {
  print "In foo\n";
}

sub findit {
  my $ref = shift;
  local(*alias);

  *stash = *{"main::"};
  while ((my $varname, my $globvalue) = each %stash){
    next if $varname eq "alias";
    *alias = $globvalue;
    if (defined(&alias)){
      if ($ref eq \&alias){
        return $varname;
      }
    }
  }
}

my $fref = \&foo;

my $fname = findit($fref);
print "ref points to $fname\n";
[download]

bryan@web ~$ ./ns
ref points to foo
bryan@web ~$