Make sure you keep in touch with the client. Use those hours so they see value. In Patrick's case, it can be as simple as creating a mailing list for clients and sending middle managers tips on industry trends, possible candidates for positions, etc.

This will also keep you from being surprised when someone wants their 10h/(month|week|whatever), and may actually prompt you to recommend how to use that time. They will pay you for leads on additional work because they see that it's a winning situation for them.