Apple has opened the availability to develop iTunes LPs and iTunes Extras to third party developers.
According to TUAW, an automatic submission process is not expected until early 2010; however, a limited process is in place which requires manual uploads.
If you're interested in developing an iTunes LP or Extra of your own, Apple has posted several resources including a best practices guide, a development guide, asset delivery tips and a testing guide.
There's also templates to get you started, and documentation on the TuneKit framework used by iTunes LP and iTunes Extras.