You cannot run an a process as a normal user then try to execute a method as elevated admin priv's. It's the entire process runs with admin priv's or none of it. This is for security reasons.
You can, however, use impersonation to execute a method as a different user, just not elevated. See
c# - How do you do Impersonation in .NET?[
^] this answer on SO. It does a great job of explaining things.