Deferred CA's with no-impersonation run as System. On Windows 2000 and greater, System uses the local computer account in ActiveDirectory for impersonation to access network resources.
The trick though, is how do you abstract something as specific as a computer account from your install to make it generic? Does your UI story have a dialog for the user to browse and select the account? If so, this context would have to have domain authentication and privs to browse objects in ActiveDirectory also. The deferred scenario has to be able to browse ( to know which object is being assigned ) and admin privs to actually make the assignment.