Found this one by accident.
1. Create a Generic Model wall based
2. Draw symbolic lines in elevation on the plane of the wall
3. Draw a long reference LINE perpendicular to the wall
4. Load the family into a new project
5. Draw two walls some distance apart (as long as the reference line)
6. Place the family on one wall with the reference line reaching the second wall
7. Watch the symbolic lines show on both walls.
Not sure what use this would have. Maybe this is already a known issue. Reminds me of detail components that sweep along invisible model lines.