Creating 2D Section Library sketches.

[stormyb]

We're trying to add a familypart with only a sketch into the 2D section library.
It is a cutout contour for a range of connectors.
So when modeling a part you can easily add that sketch and extrude it.
I've done this before with a single sketch.
Someone created a familypart of a sketch. But when I add the part to the 2D section Library (of modeling) it adds the part instead of the sketch and automatically creates an assembly of that part.
I'm stuck here, does someone knows what I have to do to fix this?
Thank you.

 

[stormyb]

Update: I managed to add the sketch, but this is the sketch of the masterpart of the partfamily. It has lost its connection to the partfamily.