I think avoiding a power struggle is the way to go.  You can't really encourage empathy by force.  And you want DS to have positive associations with church.  Maybe DH could do something with him during that time that serves a similar purpose as far as reflection or service...Nature walks?  Some kind of charity or community thing?

I know a lot of people do go to church to please family members, but I think if there's nothing there for you then it's going to breed resentment.  Hopefully there will be something there for him most of the time, friends or fun activities or Heifer Project or something.  Not trying to be the evil pagan UU influence, but I just wouldn't ever force my kid to go to church, except maybe on a really special occasion, or if they had made commitment to take part.