Slingshot has a big padded wheelie bag that says "Tour Series Golf" right on it. If they ask about it just say it is your golf bag, and if they specifically ask what is inside it (which i don't think theyl push that far) just tell them its your stuff for your golf tour (and other personal belongings) and you wont even be lying (close to it, but not) especially when considering the acronym for golf is Gentlemen Only Ladies Forbiden... or well uhh... ladies forbidden to get in your wake bag that is...
http://buyslingshotsports.com/wake/2008_wake_goods_bags.htm "Travel with your board and gear and not get charged excess baggage fees."