Dealing with tarballs that tarbomb

The scala tarball doesn't extract into a new subdirectory and instead just extracts into the directory where you run tar, i.e. a tarbomb. So in work/, you see a bin/ and a share/ directory. Is there an easy, clean way to deal with this in MacPorts? I looked at specifying some extract options, but I didn't see anything. I tried passing the ${distname} to tar -C's option to create the subdirectory, but this doesn't work, since the directory to put it in doesn't exist yet. It looks like another way is to hack it into configure to move the directories down a level, but this doesn't seem clean. Any ideas? Regards, Blair