Originally Posted by Uniter
This is a really good question ...
But yes, you should be able to do it on-line with regular reservations (it'll say, "Diamond Only" or something like that.
If you can't, look for the "Chhat" button and the Diamond Desk can help you on-line without you having to call. Otherwise... call the Diamond reservations line.
I've had best success calling reservations when you can't get in via the web. Never failed yet.