iMessage with iCloud mail aliases? Is it possible to use an iCloud email alias as the Caller ID for iMessage?

When I try to enter an alias on "Receive At > Add Another Email..." I always get an error popup titled "iMessage Activation" - "An error occurred while verifying your email". 
I've also tried to go to appleid.apple.com and enter one alias. When I press save, the page shows some loading activity but stays the same and never saves the alias. I've tested it both on Safari and Firefox. With other email addresses it works fine.
In trying what I think you are wanting to do.
I had to enter my real email address and password to activate the service.

(Remember your real apple ID youname@mac.com/*yourname@me.com* is your user name and an alias email address is NOT)

Once I did this. My apple id is used for the first email address.
I can then add another email address below it.

the second one was one of my alias emails to my apple email.

Logging out of this service will remove both addresses.