You'll need a custom stat that is "Amount Won + Rakeback" - then go to the Graphs tab, and click the Configure next to Show Session Stats. With "Sum Results" checked, double click the amount won + rakeback stat to add it to the display, then check the Show Session Stats box. There are a couple of total won (with rakeback) stats in the repository but you'll need to make sure they match the same way your site pays rakeback.