Showing all instruments from the start of a score

I am trying to make a PDF of a score with 4 instruments. Two of them do not come in before bar 45. However, I would like the system for all 4 instruments to be shown in the score from the start, not as it is now that the system for an instrument that starts later in the piece is created right before the instrument starts playing. What is the trick for doing this?

Thanks!

Tellef,

Oslo