An even shorter way than Scott's recommendation although his is accurate and effective as well, is to start a Revit session on the exusers workstation and Settings > Options change the deafult user name to the user name used by the employee. Then open his local workset file and either save to Central relinguishing his worksets or components or Relinguish All Mine in the File menu. Then make sure everyone else reloads the Central (RL) and check to see if the components or worksets are no relinguished.
Close the Revit session and reopne Revit and change the suer name back to the person using the workstation and you should be back in business. The fact is that Revit doesn't even care who the person logged into the machine really is or their username. Revit gets the username of the person logging in by default, but as you can see it is easy enough to change to any username once in Revit, no matter who you may have logged in as on that workstation. The only thing to watch out for is that you do not open the work sharing project before changing the user name in Revit and that you reset the user name afterwards.
Scott's approach is also good as I noted, but creating and eliminating the user on the local workstation may prevent access to the network if required, especially if trying to save or reload the central file, as the locally created user will have no rights in the network as a rule, ecept as a guest, possibly.
Mel Persin, AIA
AEC Technology Consultant
Technology to Visualize and Realize Solutions
Modeling the Future/Drafting the Past