I got this working with a slight variant on Fernando Camarago's solution. In my onCreate method I attach a single onTouchListener to the root view but send the view rather than activity as an argument.
findViewById(android.R.id.content).setOnTouchListener(new OnTouchListener() {
public boolean onTouch(View v, MotionEvent event) {
Utils.hideSoftKeyboard(v);
return false;
}
});
In a separate Utils class is...
public static void hideSoftKeyboard(View v) {
InputMethodManager imm = (InputMethodManager) v.getContext().getSystemService(Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(v.getWindowToken(), 0);
}