This is an unusual requirement and there isn't any clear-cut way to do it.

See Launch a Process as Standard User from an Elevated Process for one discussion of the issues involved. It gets complicated, because even with UAC users should not be logging in as members of the Administrators group. Pay attention to OTS Elevation, since that's what should be used instead and will be except on casual home users' systems where desperately trying to pretend we still live in a Win9x world is common.