There are some Lisp functions that allow you to control the annotation text of CADmep objects however controlling the leader is not one of them. Yuo can get a full list of the LISP commands at either of these links...

http://www.xtracad.com/forum/index.php/page,History.html

http://www.darrenjyoung.com/resources/autodesk-fabrication/cadmep-autolisp-function-history/

Autodesk's policy is that their API's allow you to do everything that can be done from the UI. That being said, the API's always lag behind in the abilities of the software. I don't see any API's related to annotation and/or leaders for Fabrication objects in the SDK. You can browse the documentation to see what's there by looking for the help file on your system typically located here...

C:\Program Files\Autodesk\Fabrication 2018\SDK