Refer to this Blog post, I decided to create a new one about including Hotfixes in OSD. Specially the new Release of SCCM 2012 R2 brings an annoying issue with extremly slow Downloads while on OSD (http://support.microsoft.com/kb/2910552 ; this Hotfix superseding the KB2905002 which was first used in this blog).

There are two nice ways, how to apply Hotfixes like this to the Client while on OSD, one is documented and thus supported, the other one does just work 🙂
The one that works, but neither documented or supported, is quite simple and already explained in this blogpost (http://www.m4ttmcg.com/2013/05/sccm-2012-client-push-including.html). Just create the folders:
C:\Program Files\Microsoft Configuration Manager\Client\x64\ClientPatch
C:\Program Files\Microsoft Configuration Manager\Client\i386\ClientPatch
and copy the appropriate architecture from your hotfix to one of this Folder. Do not Forget to update your Client Package to be sure using the Files with the Hotfixes.

The other way is to create a package, and copy the files with a package to the Client. First. create a package Location for the hotfix files and create two Folders named AMD64 and X86:

Now navigate to the hotfix Folder and open the Client Folder:
C:\Program Files\Microsoft Configuration Manager\hotfix\KB2910552\Client
Copy the appropriate architecture to the Package Folder, mind to delete the architecture from the file Name:
"\\servershare\Deployment\Packages\Microsoft\SCCM Client\2012 R2\CU0\AMD64\configmgr2012ac-r2-kb2910552.msp"
"\\servershare\Deployment\Packages\Microsoft\SCCM Client\2012 R2\CU0\X86\configmgr2012ac-r2-kb2910552.msp"
As example, the x64 Folder:

Now it is time to create the package, well, it’s that easy with this powershell command:
New-CMPackage -Name "SCCM Client 2012 R2 CU0" -Language "MUI" -Manufacturer "Microsoft" -Path "$PATH_TO_YOUR_PACKAGE" -Version "2012 R2 CU0"
And we don’t need to create a program, because we only use this package within our Task Sequence, but don’t forget Distribute the Package to your Distribution Points.

Make sure, that you set a Variable when formatting your System Drive, on BIOS an UEFI:
Then use this variable also to deploy Windows on the correct Drive: 
Now create a simple “Run Command Line” step in your Task Sequence, right before the step “Setup Windows and Configuration Manager” where you copy the file to a Folder on the System Drive. This Folder and the Content will remain after the Installation, so you have to delete them with another step, or leave it in the temp Directory. Here is my step:
cmd.exe /c xcopy %PROCESSOR_ARCHITECTURE%*.* %OSD_System%windows\temp\SCCMHotfix /E /H /C /I /Q /Y

Now, the last step, add the Patch to the SCCM Agent Installation, this is my Installation properties::
SMSCACHEFLAGS=PERCENTDISKSPACE;NTFSONLY SMSCACHESIZE=10 SMSMP=$FQDN_MP FSP=$FQDN_FSP PATCH=C:\windows\temp\SCCMHotfix\configmgr2012ac-r2-kb2910552.msp

If this is not working, you named the subdirectories wrong in your package, or you forgot to remove the architecture from the files.
Hope this helps, Martin