The SingleProblem pattern is based on demonstrating the value of the wiki by using it to solve a single problem. Once the problem is solved people see the value of using the wiki and will want to use it for other problems, projects, etc.
Ask people if they have a problem requiring collaboration to solve it. If so, offer to help solve it using the wiki.
Use a wiki as a standard place to put things and compare them side by side - Mark Dilley did this with union contracts1)