I don't know for the lock screen but for the login screen it is possible. But not as simple as it should be.
Follow the instructions on this page.
It involves changing the registry key
Enabled to 1)
The problem is this change does not survive at the moment a user logs in. So there are also instructions to change this value after every login with a batch file and the Task Scheduler.
The batchfile should be like:
REG ADD HKLM\SOFTWARE\Microsoft\Windows|CurrentVersion|Authentication\LogonUI\UserSwitch /v Enabled /t REG_DWORD /d 1 /f
Run this file with a task in the Task Manager "at log on" of "every user".
Exact steps (with screenshots) are at this page.
I found a way to do the same when you get the lock-screen in case of inactivity.
I discovered that when you disconnect with "Remote Desktop" you get the full-Switch-User-screen with all users. You can simulate this with the command
tsdiscon.exe. We work from there... (You can test this command manually)
Now create a normal-"scheduled task", name it
Switchusers. In the trigger-tab set a trigger on
On workstation lock. In the action-tab set an action to run
tsdiscon.exe. Press Ok.
Now, whenever you get the lockscreen,
tsdiscon.exe is executed and you get your full-switch-users ;)
If for some reason this doesn't work you can also create the same task with trigger
On idle and set the
Start the task only if the computer is idle for on you desired idle-time and
Wait for idle for on
Do not wait and check
Stop if the computer ceases to be idle (or else you'll get multiple login-screens after longer time-outs)