Start a process with elevated privilege<>
This question already has an answer here:
Please see Elevating process privilege programatically.
You either need to throw a UAC Elevation prompt (potentially annoying) or run your root forking process as administrator. By declaring it in the ClickOnce or program manifests, you can ensure that simple double-clicks on your executable will automatically prompt to elevate.
If the end user's machine has UAC enabled, at some point some kind of prompt will appear, as there is no legitimate way of elevating a child process from an unprivileged one.