Its possible to do this in the bootstraper of Nancy
protected override void RequestStartup(TinyIoCContainer container, IPipelines pipelines, NancyContext context)
{
//CORS Enable
pipelines.AfterRequest.AddItemToEndOfPipeline((ctx) =>
{
ctx.Response.WithHeader("Access-Control-Allow-Origin", "*")
.WithHeader("Access-Control-Allow-Methods", "POST,GET")
.WithHeader("Access-Control-Allow-Headers", "Accept, Origin, Content-type");
});