I was looking over some of the options on my CO 360 MM account that I recently opened to get the $500 bonus, and I noticed that they have now added a link to add beneficiaries. I can only confirm this for the 360 MM since I have no other accounts with CO.
When you log in click on "View Account", followed by "Account Services & Settings". When the pop up box opens select "Manage Beneficiaries " and follow the prompts.
I went through the process and it requires the following information for each beneficiary: Name, address, state, zip, SSN, DOB to be entered into the online form. The process was easy and straight forward.