If you are going to add it in as a fermentable, you will need to know the approximate sugar content to get the properties correct. Don't know it, you can always wing it and then make a correction for next time if you find you are off.
Adding it is pretty easy. Click on 'fermentables' in the ingredients listing. Up on the ribbon bar there will be a button to 'add fermentable'. Click on this and fill out as much of the info as you can figure out. You can use some of the juices already in the database to help with the figures you may need to get it started.