Local Staff for Brass from Balcony

Stealing an idea from Respighi (who probably stole it from Mahler), I'd like to have brass (2 trumpets, 2 french horns, and 2 trombones) play from the balcony during the finale of a piece that I'm scribbling.

I would imagine that one way to score this would be to add an additional part to each trumpet, horn and trombone staff. But Is there a way that I could create a local staff - i.e., an extra set of staves that appear only during the finale? I did not see anything under the "Add" menu that would enable this.

What I'm currently doing (attached image) is adding extra parts to the trumpets and trombones, but this wont work for the horns, because the parts will be divided amongst Horns 1 and III and II and IV. I don't see how I could add another voice. I tried Add->Interval->Unision, but for some weird reason, where the note is an accidental it added a note a half tone above. (Yes, I checked to make sure that I didn't inadvertently add "second above")

Thanks