multi screen/windows in one project.

I often find myself coding across both my monitors and have one bugbear.
Scenario.
Open project.
Shift+Alt+3 give me nice usable cols
Find I need to view a few more file at the same time Ctrl+p open file.
Drag over to screen 2.
Shift+Alt+3
Now I have 6 cols to play with yay!

My problem is that the new window is not a child of the first so I can't Ctrl+p there I have to return to the original window open the file and drag it to window 2.

It would be great if window 2 could be part of the window 1 project.