RouteParameters param = new RouteParameters();
param.UseHierarchy = false;
The problem with not serializing-out useHierarchy=FALSE parameter was addressed in latest release of WPF SDK 1.0 (June 2012, assemblies versioned 3.0). Please try it.
If you cannot upgrade to the latest WPF SDK, there is a workaround:
Basically you�??ll need to define the full url to the operation in the route task, set the useHierarchy parameter manually, and include a placeholder to neuter the addition of the operation (e.g. Solve) by the API.
Hope this helps,