Hello,
You can build a custom stat to track your rewards if they are based on a percentage of rake, however most sites now use additional personal metrics making it impossible for us to build anything general (and for many sites, impossible for you to even track your own results as it's based on an unknown factor).
That said, if you have all of the relevant information about how it is calculated you can build this as a custom statistic and put it on your graph. See
this guide for the basics on custom statistics creation and
this guide for a deeper walkthrough. The latter was written for PT3 but the techniques all apply to PT4, the interface is just slightly different.
There are also a few custom stats in our
download warehouse for free download that work in this general fashion and they may be a good starting point for you (just search for rakeback).
-Kraada