Pasting the code is suitable only for small extensions, mine is medium-size, has many source files and I can't imagine installing it such way.
I believe there was a trick which would overcome tgz upload restriction - some years ago, I've seen text-format archives inside unix shell scripts, which can be extracted with bash (or maybe even just sh) - probably just MIME decoding then passing to tar/gzip. Then, such file can probably be uploaded with different extension, while at documentation page one would ask to rename and run the file after a download.
But anyway, I've choosed a _free_ hosting for my extension, I hope the hoster won't delete it any time soon. Just an external tgz link.
Is there some reason your extension can't be hosted on wikimedia's svn? Is it not freely licensed?
V/r,
Ryan Lane