dd if=/dev/zero of=./foo count=1 bs=1 obs=9 seek=1

obs=BYTES
          write BYTES bytes at a time (default: 512)
   seek=N skip N obs-sized blocks at start of output

>ls -l foo
-rw-rw-r-- 1 user user 2 Mar 28 16:05 foo

dd if=/dev/zero of=./foo count=1 bs=1 obs=1 seek=9