Check out this web site: http://www.bentolunch.net/ or also http://lunchinabox.net/, or also http://mothering.com/back-to-school for tons of suggestions for fun and healthy lunches.
Some are "kind of" sandwiches, but I bet they will not be perceived as sandwich.
Even if you don't go as far as making some of those adorable creations every day, I would also suggest that you make your own lunchables, that is so much more cheaper, and you can mix it up a lot more: different kinds of crackers or chips, different kinds of cheeses and lunch meat, many more different combinations possible.
And get a large opening thermos, and you can send hot foods with him, too. They will easily stay hot for a few hours until lunch time.
Have fun thinking a bit outside of the box, and with the fun presentation of the food you can find on those web pages, I would surprised if your son will not end up eating foods that he may otherwise refuse to even try.