Hiding old data from new users

[Bob Eby]

Hi Mercurial experts,

This may sound strange but we've checked a secret into one of our
repositories and now we want to share pretty much everything but that
with an outside consultant.

I tried creating a partial repo of a "cleaned" branch with:

hg clone -b

Problem is, this included all the parents which pulled in the old
default branch that had the secret.

Aside from copying a current checked out file set into a brand
spanking new repository, is there a way to create a partial repository
suitable for intermediate push/pull upstream from client repositories
that can act as a "secrecy buffer" against some old default file?

I'd like to give them some but not all of the repo history, or does it
not even make sense to want to share that extra history?

Thanks for any and all input,
Robert Eby