Is it not sufficient to run the service pack silently? Pass /S (note: Captial S, /s will not work) as the argument to the service pack executable.
For new installs, could you not create a batch script that first runs the deployment, then runs the service pack afterwards? A batch script to do this would look something like this:
pushd *setup.exe folder*
setup.exe /Script /Wait /Language en-US *deployment_inifile*
popd
service_pack.exe /S
Andy
Autodesk Employee