When user switching, KNetworkManager complains it is already open and asks if I want to start it when I start KDE. I assume this is because I edited /usr/bin/startkde to have it start KNetworkManager with KDE according to the instructions at thread #87443.

Prior to this I had been using Wicd, I had it set to start at boot via rc-update add wicd boot and it would be open in the tray when I started KDE. User switching would still have it open in the tray. I would like the same experience with KNetworkManager and I assume that I configured it incorrectly. What is the right way to configure it so that it behaves like Wicd did?

This is due to the architectural design of NetworkManager, which can only handle one client providing settings at any one time.

If you are using the Network Management applet, then simply unloading the daemon when switching user ( then reloading it again when switching back ) would be all that is needed.

Note that this will cause any active connections to be severed.
Ideally KNetworkManager would watch the active console using ConsoleKit and release appropriately.