I can think of several ways and you will probably see other posts here with more ideas:
Write a batch file - Run office, then use REG ADD, etc...
Script, pick your poison - Vbscript, Autoitscript, Package Builder, etc... Same thing Run Office with wait then run the function to modify the registry keys. Trap the return code from office setup and exit with that return code.
Think backwards -Create a distro package that has Office as the prereq and the package that makes the modifications as your main package.
Continue to try and do it within the Orifice setup.
Coatesish- Create a custom vulnerability.
Hire brainwashed spider monkeys to go around at night with thumb drives in ninja outfits. Ninja outfits optional but highly recommended.
I would have to disagree with zombies.
Their upfront purchase cost looks good, but the cost replacement parts is murder!!
Mark Star - http://www.marxtar.com
Home of Power State Notifier and Wake-on-WAN for LANDesk