Open regedit.exe, go to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList
On Windows 7 the two last keys SpecialAccounts and UserList may not exist and you will have to create them.
Under UserList, create a new 32-bit DWORD value and name it with the user Login, set value to 0.
Create a new 32-bit DWORD value for each user, in case you have more.
Thats it.
In the case the user is still being displayed, open secpol.msc, go to Local Policies\Security Settings, find the entry Interactive Logon: Hide last user and switch it to Activated.