Backing up the Encryption Key with Powershell

Hi,

I need to automate the backup of the encryption key of SSRS with Powershell.  I tried wrapping the application rskymgmt with no success.  Then I found out that you could do it with the WMI class as mention here: http://msdn.microsoft.com/en-us/library/ms155048(v=SQL.100).aspx#CommunityContent. How would I do that in Powershell, all my attempts have failed!

thx in advance.