Can't you take te same approach ClojureScript took, i.e. to generate a straitforward translation to JavaScript, and then let Google's closure compiler take care of the optimizing thing ?

For instance, for this Roy generated JS:

    var True = function(){};
    var False = function(){};
    var getBool = function(b, ifTrue, ifFalse) {
        return (function() {
            if(b instanceof True) {
                return ifTrue;
            } else if(b instanceof False) {
                return ifFalse;
            }
        })();
    }

The Closure compiler generates:

    var True = function() {
    }, False = function() {
    }, getBool = function(b, c, d) {
      var a;
      b instanceof True ? a = c : b instanceof False && (a = d);
      return a
    };