I am also curious as to how to do this. I often use high voltage parts in my designs whose nets are "in the air" (i.e. they don't touch the board). It would be very useful to be able to place a part outline with reference designator, even though it isn't listed as connecting to anything in the netlist.
We have maybe a similar problem, in that we require a barcode label to be placed on our boards.
The way we do this is define a mechanical cell.
Goto Cell Editor
Then select your required partition (e.g. labels)
Then on the second tab is the Mechanical cell option (select this)
You can then create a cell which has no pins, you can add the required graphics and route/plane obstructs as required.
With your pcb design, goto Setup then Library Services.
Select the Cells tab.
Then you can import your new label cell from the new Labels partition.
This then adds to the CellDB partition within the design.
Then you go through Place Parts and Cells dialog and from the Criterion drop down menu select Mechanical Cell.
Your new label will then be available to place on your pcb as if it were a regular component.
In our designs we also use this method for High Voltage warning labels and Antistatic warning labels.
We get exact the same question from our customer and are puzzeling how to achieve this.
So far without success.
I wondered if in the meantime you have found a solution to solve the issue and would appreciate it if you could share it with us.
Thanks in advance.
The working method you describe is also familiar with us and works great for placement in the layout only, but now the designer wants to place the mechanical part already in the design phase in the schematic.
Then as far as I know the mechanical part has to be replaced by a package part, including a pin and RefDes as mandatory properties.
Do you have any experience with this?