Only way to do that is to place the units as yours, but as p9-p12 and then given to you...
You can't disable your vision of yourself fast enough with triggers before you can see the vision your units give you in the beginning of the game.
Can't get the units to appear when placed.
ADDITION:
Ok, I was able to find the Player 9 triggers on the site. I imported them into my map and made sure that the boxes beside each condition or action were checked. Will I now be able to place Player 9 units on the map?
You need a real editor, such as SCMD. Get it from the DLDB.
In there, there's a little drop down list thaty says Player 1. Change it to 9, and place your units. Or, you can place units for anyone, then open up properties for those units, and give them to player 9.
Also, you can't create units for P9-12 with triggers. You have to create them for someone else, then give them to whoever you want to give them to.