I have been using Partition Magic (PM) for this.
You can make dummy partition and HIDE it.
All done in PM. And it worked ok.
I have been making hidden partitions not only at the
beginning or end of HDDs, but also in the middle of it.
The problem is that partition prgz SEE that hidden partition
in some way, so you didn't really cut away the bad part, but
only hid it from user and OS. If you use it for your HDDs,
then no problem, but you can't fool other people giving them
"100% working" hdds, becouse they can see these hidden
partitions. If they know how, of course
.