Like Greg said, a mechanical cell is a good way to do it. No, it will not appear on the BOM unless you are using an older version of the tools. ~EE791.
In these older versions the Forward to PCB symbol property was ignored by the partslister. Subsequent partslister versions exclude any symbols that have that property set to False.
- I would suggest creating a complete part (Sym, Cell & PDB) with the Cell being a dummy. Create a mechanical cell that is accurate.
- Place the symbol that carries all of your properties so it appears in the BOM/partslist.
- Place the mechanical cell in Expedition and leave the Cell associated (dummy one) with the symbol unplaced.
The down side is you have to suffer a DRC error, but you can accept that. Another drawback/feature? is the symbol and the mechanical cell have no association, so changing one will not affect the other.
Good luck.
Mike