I'm guessing it may be even smaller than a file filled with zeroes. If I were doing it, I'd use a sparse file, so it only takes a few blocks, but (sans compression) would take a long time to download. Like this:

  tsuraan@macbeth ~ $ dd if=/dev/zero of=abigfile bs=1M count=1 seek=1000000
  1+0 records in
  1+0 records out
  1048576 bytes (1.0 MB) copied, 0.00320282 s, 327 MB/s
  tsuraan@macbeth ~ $ ls -lh abigfile 
  -rw-r--r-- 1 tsuraan tsuraan 977G Sep 16 11:18 abigfile

I probably wouldn't actually make it ~1TB, but that's the idea.