Hi,

You can add whatever fields you need to the indexset you are using, and then populate them by hooking up to the GatheringNodeData event of your index provider:

using Examine;
using Umbraco.Core;

namespace App
{
    public class ExamineHandler : IApplicationEventHandler
    {

        const string INDEX_PROVIDER = "ExternalIndexer";

        public void OnApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {

            ExamineManager.Instance.IndexProviderCollection[INDEX_PROVIDER].GatheringNodeData += (sender, e) =>
            {
                // get data from other content...

                // add field key and data
                e.Fields.Add("KEY", "VALUE");

            };
        }

        public void OnApplicationInitialized(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
        }

        public void OnApplicationStarting(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
        }
    }

}