In 2006 BEP 47 Padding files and extended file attributes was published. As soon as torrents contain TTH for every file and info.pieces is not required, one can manipulate files freely. The sample can be viewed here: for any folder the webserver is able to construct both dcls and torrent descriptions.
Unfortunately, this BEP was not widely implemented, so such an easy thing (in more mature p2p protocols like ADC and G2) is still not possible with most BitTorrent clients.
Also, in my practice current "info.files.path" approach is a big waste because nested directory names are repeated way too often. My GreyLink DC++ share has roughly 6800 directories. Its description in dcls format (that is, xml.bz2) is roughly 3.1Mb big. Unpacked XML is 12Mb. Being converted to .torrent format (following BEP 47) it becomes 16Mb big despite XML having TTH in Base32 and torrent having TTH in binary form.
Thus, some kind of nesting would be helpful to avoid repeating path fragments. I guess, there should be another BEP for nesting "info", and this would probably also allow what you want in another way.