Ok so there is a way to do this in fact we use this method where I work.
Dell activates windows using a certificate and a bat file on it's OEM installation disk.
first you will need to copy the OEM cert and SLP.bat files from your Dell OEM CD.The OEM Cert is located on the CD under sources\$OEM$\$$\system32\OEM and is called OEM (XrML Digital License). slp.bat is located under sources\$OEM$\$$\setup\scripts.
Then save them to your deployment share.
Currently it should look something like this:
cscript %windir%\system32\slmgr.vbs -ilc %windir%\system32\oem\OEM.xrm-ms
cscript %windir%\system32\slmgr.vbs -ipk 32KD2-K9CTF-M3DJT-4J3WC-733WD
but seeing as our OEM folder will be elsewhere we will need to change it to this:
cscript %windir%\system32\slmgr.vbs -ilc OEMLOCATION\OEM.xrm-ms
cscript %windir%\system32\slmgr.vbs -ipk 32KD2-K9CTF-M3DJT-4J3WC-733WD
In your answer file under the OOBE pass in your answer file add:
Microsoft-Windows-Shell-Setup_neutral
FirstLogonCommands
SynchronousCommand(Order="1")
Action- AddListItem
CommandLine- \\server\share\dellcert\makeOEM.bat
Description- Make OEM Folder
Order- 1
RequiresUserInput- True
SynchronousCommand(Order="2")
Action- AddListItem
CommandLine- \\server\share\DellCert\copyslp.bat
Description- Copy slp.bat to share folder
Order- 2
RequiresUserInput- True
SynchronousCommand(Order="3")
Action- AddListItem
CommandLine- \\server\share\DellCert\copycert.bat
Description- Copy Dell Cert
Order- 3
RequiresUserInput- True
SynchronousCommand(Order="4")
Action- AddListItem
CommandLine- \\server\share\DellCert\Runslp.bat
Description- Run slp.bat
Order- 4
RequiresUserInput- True
The only way I was able to get it to work correctly was by braking it up into 4 parts as shown and set RequiresUserInput to true (don't ask me why it just would work otherewise
I actually posted more details about this else where: http://starvinggeek87.blogspot.com/2013/05/useing-windows-deployment-service-to.html