Building package from newer upstream source?

[Stuart Ballard <sballard@netreach.net>]

For a couple of reasons, I have a need to install versions of Xfree86
that are newer than the newest available packages. In fact, I want to
get the newest version from XFree86's CVS repository.

However, I'd like to do this in such a way that I don't break the
careful Debian packaging done by the XFree maintainer, and in a way that
means future updates get handled automatically (once the newer versions
get Debianized).

My theory is that it should be possible to do something along the lines
of the following steps:

1) Download .dsc and .diff.gz files
2) Get XFree source from CVS
3) Invoke some dpkg magic to turn these components into a bunch of
packages with a custom version/revision number
4) Install the resulting packages with dpkg -i.

I believe that step 1 can be achieved with apt-get's "source" option.
Step 2 is fairly simple except that I don't know whether the source as
checked out of CVS is in the exact right format to be patched by the
diff.tar.gz. I have no idea at all about step 3, and I couldn't figure
it out from the Packaging Manual
(http://www.debian.org/doc/packaging-manuals/packaging.html/) either.

Can anyone help?

Thanks,
Stuart.