You could add a custom class called "myRadio" to the field and do something like this,

$('.myRadio input[value="Yes"]').click();

In my experience, triggering the click event has been the only way to get everything to behave properly. Changing the "checked" state directly doesn't appear to trigger some of the other events Forms attaches to the field.

Note that if you assign values to the choices, you would use those values instead.