The best outcome:
secpol.msc>>Security Settings>>Security Options>>Interactive logon

o
not display last user name
deatails 'Do not display last user name Windows setting
(dontdisplaylastusername)'
(
http://www.maxi-pedia.com/do+not+display+last+user+name)
There is way to hide only second account but if you will do impossible
will be to log on this account...
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Flavius