I am quite surprised this isn't available since there is a custom formula field in the CM gradebook template when you create a new column but its' greyed out... Currently only able to use the pre-defined calculated columns which is extremely restricting. I think this is more of a bug rather than an idea to be honest.
Hello Joseph,
The Formula Builder functionality for Curriculum Manager is currently in development. There will soon be updates regarding this feature alongside the ability to sync to gradebooks from curriculum manager soon.