Positioning new staff

[Paul Hodges]

I can't find anything bearing on this, I'm afraid.

I am writing out a piece for two pianos; so there is a grand score 
containing two piano scores.  I need to add a third staff to the first 
piano part for just two bars.  It will be under the two staves already 
existing.  I can add the necessary staff, and it has the correct music 
on it - however, it is positioning itaself under the second piano (and 
drawing barlines right through):

How can I make the extra staff appear in the middle where it should be?

Thanks for any suggestions,
Paul