This is the workaround:
- In the Project, create detail lines that describe the elements you want to copy
- Make New Family - Generic Profile
- Copy the detail lines in the Project (Ctrl + C)
- Paste them into the Profile family (Ctrl + V)
- Open / create the other family you want to put those lines into
- Copy them from the Profile family into the other family (lets say it is a Planting family). They will appear as model lines in the Planting family. Yay!
Sure, this method has some limitations, but it is a valid workaround in a lot of situations.