Make it look like it's their idea
At the end of the day though, i find that the best way to get them to do what you want, is to make them feel like it was their idea in the first place. That's probably the most valuable trick to learn. I know that seems like we lose the credit for the catch but we're engineers right? We usually don't get recognition unless something goes terribly wrong:)
(Rick Marry in a comment to How do you get open source frameworks past the red tape? )
That's very well said. It is indeed the most valuable trick you can learn in order to prevail in many situations in the corporate world. Although some developers or engineers might want to disagree at some point we all are sales people as well. Probably as a true consultant you are more a sales person for ideas than you are an engineer. So your people skills and your ability to circumvent blockades is a key element for doing your job well.