If you use a foundation form board, you can also spread the bottom bar away from the top bar with a spacer. This pulls the side bars in a bit. When your done wiring, remove the block and the frame will go back to it's normal shape and tightens the wires.
Unfortunately I haven't gotten that far with my frame assembly videos, but it will be coming
The tighter the wires the better, but even loose wires are much better than no wires.
Where did you buy your frames? I've never seen frames that weren't already pre-drilled for wires.