RewriteCond %{HTTP_HOST} ^([^.]+)\.nanosouffle\.net$
    RewriteCond %{REQUEST_URI} !^(.*)\.pl$
    RewriteRule ^/(.*)$  /usr/local/www/nanosouffle/%1/data/$1 [L]
    RewriteCond %{REQUEST_URI} ^(.*)\.pl$
    RewriteRule ^/(.*)$ /nanosouffle/%2/data/$1 [PT]

...
    AliasMatch ^/nanosouffle/(.*)\.pl$ /home/www/perl/$1

# It is apparent that %2 (of HTTP_HOST backreference) is not being substituted in the RewriteRule here -- any ideas?