Ajax is not designed to be used outside of profile. Anywhere else it will simply just display the value. If you're using CB 1.4 you can now specify Default, Output, Formatting, Reason. The below maybe able to achieve what you're wanting.
[cb:userfield field="FIELD_NAME" /]
More on substitutions at the below link. Again the ajax is designed for profile and userlist usage only. You may need to change the reason to List in order for the ajax to load in, but it should do so with the above assuming it's supported.
www.allmysocials.com/tutorials/item/233-substitution-usage