I have a virtual component (pipe).  We will be spec'ing the length as part of the part number in the BOM, and the part is driven by a length property in the assembly.
 

We have it working (kind of) by creating a design table in the virtual part, and using excel functions to join our "root" number, along with a formatted text.

example: Our "root" number is 1XXXXXX, and the length (18 inches) needs to be