It seems like that problem is needlessly being complicated by conflating key extraction and sorting. (This was an issue that was discussed on perl6-language about the current sort operator — how do we make it possible to isolate the extraction code from the actual sort order, which should then be possible to request declaratively?)

sub order_of_sorted {
    my ( @num, @suff );
    for( @_ ) {
        m/ \A (\d+) \. (.*) /x or die "malformed data";
        push @num, $1;
        push @suff, $2;
    }
    sort { $num[$a] <=> $num[$b] or $suff[$a] cmp $suff[$b] } 0 .. $#_
+;
}

for my $outer ( ( values %hash )[ order_of_sorted keys %hash ] ) {
    for my $inner ( ( values %$outer )[ order_of_sorted keys %$outer ]
+ ) {
        # ...
    }
}
[download]

If you want to store the data rather than output it, you can transform the nested for-loops to an equivalent chain of maps (but note that that doesn't make it an ST).

I know which version I'd prefer to maintain, even though this is probably slower than your GRT.

Update: the following, which I originally wrote, is obviously wrong:

   for my $inner ( ( values %$outer )[ order_of_sorted keys %$inner ] 
+) {
   #                        ^^^^^^^ Correct.                ^^^^^^^ Oo
+ps.
[download]