Where did you hear from that unattended install only supports per-seat licensing mode?

There is a known issue with unattended install using pre-processor licensing. See Q273769 - FIX: SQL Server Setup May Fail If You Select Per Processor Licensing Mode

(http://support.microsoft.com/?id=273769)

So, if there is a fix for it, my guess is that using unattended install with per-proc licensing is supported.

RS