Ability to create custom drop down with values from another custom field in another workspace

I would like to create a custom drop down field that appears on all Epics that use a shared layout. The custom field should be the available values in another custom field for a specific workspace.

To illustrate:

* On workspaces 1-10, I want to add custom dropdown field “projectcode” to all epics in those workspaces (I know how to do this).

* The available values in that custom dropdown field should be derived from values in custom text field “codename” for all of the features in workspace 20.

** Workspace 20 might have 35 features today

** The custom text field for Workspace 20 will be unique for each of the 35 features

*** Feature 1 will have Codename-1

*** Feature 2 will have Codename-2

*** Etc…