I would just use opendir and readdir recursively to scan the subdirectories yourself, and save the subdirectory only when it doesn't contain any subordinate subdirectories.

For example:

use strict;
use warnings;
use FileHandle;

my $h_dirs = terminal_subdirs("/tmp/a");
my @dirs   = sort keys %$h_dirs;
print "Terminal Directories:\n", join("\n", @dirs);


sub terminal_subdirs {
    my ($top, $h_results) = @_;
    $h_results ||= { };
    my $fh = new FileHandle;
    opendir($fh, $top) or die "Arrggghhhh -- can't open '$top' ($!)\n"
+;
    my @files = readdir($fh);
    closedir $fh;
    my $nsubdirs = 0;
    foreach my $fn (@files) {
        next if ($fn eq '.' or $fn eq '..');
        my $full = "$top/$fn";
        if (!-l $full and -d $full) {
            ++$nsubdirs;
            terminal_subdirs($full, $h_results);
        }
    }

    $nsubdirs or $h_results->{$top} = 1;
    return $h_results;
}
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