One way to get soft light outdoors without using bounce flash or a light modifier such as an umbrella or softbox is to shade the subject.
In the test shot above, the ambient light was not ideal because of the shadow patterns on the subjects' faces. Here's another view illustrating the same issue:
Adding fill flash to lift the shadows mitigates the issue a little but doesn't solve the problem in this case because the highlight and shadow pattern is still visible:
If the ambient is dim enough, it's possible to delete the ambient completely and use flash alone to illuminate the subject.
In this case, however, I decided simply to use the menu to block the light on the subjects. The resulting shade results in soft light on the subjects while removing the distracting highlight and shadow pattern.
This technique will result in a brighter background -- you may want to factor that into your decision whether or not to use this technique. Here, I didn't mind the overexposed background.