Some codecs are specifically left out of the install for a reason. Careful you don't sidestep the legality by having proprietary things from the get-go.

Instead, perhaps an easy-to-use installer for them. BTW, you never said which version you were looking to base the project on. Feisty Fawn (and I imagine Gutsy Gibbon) already have a point-and-click codec installer.
On the topic of easy-to-install things, how about Frostwire and Beryl? Are you familiar with the Nvidia Installer in Feisty? Maybe something just like that for those two.
--Jay