I just tested this method with my October on PP and it came out to be $20 off $12127 was the actual MRG and I calculated $12107.

To do this I filtered for only my PP hands in the month of Oct using the Preferences tab. Then I went to the summary tab and took the "Total Rake" column and divided it by the "Players" column, this will give you apprx. your share of the rake on a site that uses the Party Poker rake calculation. To figure your rakeback you just multiply your share of the rake by .25 or .35 or whatever % your rakeback is.