Sorry I got it. For anyone else stuck on this.
Here is an answer.
var options = new dojo.data.ItemFileWriteStore({ data: { identifier: 'name', items: []} });
s = "ALL BOUNDARIES";
options.newItem({ name: s });
s = "";
var count = map.layerIds.length;
for (var i=1;i<count-1;i++)
{
var layerName = map.layerIds;
var layer = map.getLayer(layerName);
if (layer.visible) {
options.newItem({name:layerName});
}
}
var combo3 = dijit.byId('selectBoundary');
combo3.attr('store', options);