You should be able to set up a stat like any of the other count-type stats (most of them) in the 'holdem cash player statistics' section, using "sum".
You will need the 'holdem_hand_summary.amt_rake' database field, and if you want only hands you won then 'holdem_hand_summary.id_winner' or 'holdem_hand_player_statistics.amt_won' will be useful.
See the Custom Statistics
Documentation and the
Custom Statistics and Reports FAQ for walkthroughs.