[nikita.mmf]

например так

(function ($){
var galleryId = 0;
$.fn.stepCarousel = function ( options ) {
  return this.each(function(){
    var id = this.id;
    if ( !id ) { id = this.id = 'gallery'+galleryId++; }
    stepcarousel.setup( $.extend({}, options, { galleryid : id }) );
  });
}
})(jQuery)