Auto Logon Kiosk Controlled via Group Policy

I have several Windows Vista kiosk machines that are joined to my domain.  I would like for these machines to automatically logon to my specific domain using a specific user account every time they are turned on.

In order to do this I have used Group Policy Preferences to set the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon

• AutoAdminLogon
• DefaultDomainName
• DefaultPassword
• DefaultUserName

Unfortunately this method is not secure since the DefaultPassword is sent in plain text and resides as unencrypted text on all machines that are affected by this GPO.

To help keep this as secure as possible the user account has been restricted to have lowest possible permissions and is only allowed to login to specific machines.

Are there any alternative methods to have an auto logon in a Windows Vista environment controlled using Group Policies?