Hi Don,
Create Organization Unit (or some other level at which you will apply Group
Policy). Move all your users that you want to disable lock workstation to
this organization unit (OU).
Create new Group Policy (GP) connecting it with OU. Click edit GP and expend
user configuration -> Administrative Templates -> System -> select
Ctrl+Alt+Del option -> double click Remove Lock Computer and select Enable.
Click OK and close Group Policy Editor.
Hope this helps you solve your problem.
Mike