What version of SE are you using? It looks like maybe ST6 or before? The capability you are after is called "reference text" and it was new in ST7.
Sorry, but no dice. We can't release functionality in MPs. Plus this was a huge project and it was only tested in ST7 along with all the code changes there -- so it would not be feasible to put in ST6 and redo all that testing.
If that's the parts list item number, you can already do that in ST6 (and earlier).
On the Callout properties page click the Property Text button, then select From Graphic Connection, then select Parts List Item Number from the list.
Use the Save As to retain for later use.