I feel your pain. I've worked with some very large companies, and getting anything done, especially content generation, was a slow role.
You're always going to be dealing with a "committee" with a larger company.
I worked with a large healthcare client on their blog, among other things. To get them going, I would do the research and come up with ideas and topic summaries for them to then write from. Granted, it was more work for me, but after a while they started catching on and getting more proactive.
Plus, it helped when they saw the positive effects as a result of some of the content (specifically in the social realm).