Design the path of least resistance. Make it easier for them to complete the task than to put up with you. Set up a regular schedule of phone calls, emails, courier pigeons, or your preferred method of communication. Become a consistent (but still polite) annoyance in their lives until the task is completed.
They are right on here, and so many design professionals don't realize that they have to be creative and design things in all areas of business. Design strategies, design methods of communication, design workflows, design presentations... you get the idea.
One thing I'll add to number 4 on their list: Don't put the recipient's name in the To: field until you are actually ready to send the email. I've seen this strategy go wrong before, and this is one way to make sure you don't send the email you never intend to.