My HO is that having three linked forms with

1. a file selector panel that copies the files to a temp directory
2. a tar-gzip-er,
   and then,
3. an upload-the-tgz-file button on a MIME multi-part/form-data page

is the easiest and most usable solution. Since even Doze zunzip programs now understand tgz, you're not harming his productivity (or our Internet bandwidth) as much as individual uploads would.