How to extend the Windows Server 2008 evaluation period?

1.Click Start, and then click Command Prompt.
2.Type slmgr.vbs -dli, and then press ENTER to check the current status of your evaluation period.
3.To reset the evaluation period, type slmgr.vbs ?rearm, and then press ENTER.
4.Restart the computer.

I have been this procedure but i only get 10 days of grace period instead of 60 days. Is there any other way on how to extend the evaluation period for a longer span of time?
I would really appreciate for any help from you guys.
Thank you.