Configure your apt-get

 Set up your /etc/apt/preferences as follows:

 Package: *
 Pin: release a=stable
 Pin-Priority: 1001

 Package: *
 Pin: release a=testing
 Pin-Priority: 60

 Package: *
 Pin: release a=unstable
 Pin-Priority: 50

add the stable sources to /etc/apt/sources.list

Run apt-get update

Run apt-get dist-upgrade
Ignore this warning:
WARNING: The following essential packages will be removed
This should NOT be done unless you know exactly what you are doing!
  libstdc++5 (due to apt) dselect (due to dpkg)
1 packages upgraded, 2 newly installed, 130 downgraded, 11 to remove and 3 not upgraded.
Need to get 10.8MB/32.9MB of archives.
After unpacking 39.5MB disk space will be freed.
You are about to do something potentially harmful
To continue type in the phrase 'Yes, do as I say!'
?] Yes, do as I say!

This will fail somewhere during the downgrade.
Don't worry about this, I had to manually allow overwriting:

dpkg --force-overwrite -i /var/cache/apt/archives/debconf_1.0.32_all.deb
dpkg --force-overwrite -i /var/cache/apt/archives/dpkg_1.9.21_i386.deb
dpkg --force-overwrite -i /var/cache/apt/archives/shellutils_2.0.11-11_i386.deb
dpkg --force-overwrite -i /var/cache/apt/archives/fileutils_4.1-10_i386.deb 
dpkg --force-overwrite -i /var/cache/apt/archives/e2fsprogs_1.27-2_i386.deb
dpkg --force-overwrite -i /var/cache/apt/archives/sysvinit_2.84-2woody1_i386.deb
dpkg --force-overwrite -i /var/cache/apt/archives/logcheck_1.1.1-13.1_all.deb
dpkg --force-overwrite -i /var/cache/apt/archives/debianutils_1.16_i386.deb

apt-get -f install

and continue with ->
 
apt-get dist-upgrade
until there are no more packages to be downgraded.

Next, do the forced downgrade of libc6 (which causes almost all non-stable to be removed)

apt-get install libc6    

run:
apt-show-versions |grep -v /stable 
and look for packages that are not updated. Update them manually or remove them

This should do it