You could provide your gambling log and note page 1 of the
Instructions for issuing Forms W-2G that note when W-2G's are issued (they're not for poker cash games), and additionally note that because when you're playing poker cash games you're playing against other players (rather than the casino), the casino does not keep track of who wins and who loses in poker cash games. You could also ask at your casino whether someone on staff would be willing to sign an affidavit where they acknowledge that they don't keep track of players' results in poker cash games.
-- Russ Fox
