Place it as a drawing. The layers will not be added but you can still control them in the settings dialog for the drawing. This can actually be a big advantage in some cases because the drawing's layer settings are unaffected by layer combinations.
The lines etc are all still detectable/snapable so drawing over the top should be no problem. The only limitation off the top of my head is that the magic wand doesn't work (it finds the boundary of the drawing).
Edit: If you need to actually modify the drawing itself you should probably open it in a separate session of ArchiCAD.