So you have a local business which does a specific service type but that service is not amongst the predefined Google Local categories, although there is a much less specific parent category, what is the plan of attack? Let's say the closest relevant parent is called "gizmos" but what you offer is "mechanical widgets". Use the parent and perhaps detail the specialty in the description? Will surfers searching for "mechanical widgets myville" find the listing or would they have to also enter gizmos?