There's only really two options...
1) Don't work with the portal.
2) Work with the portal and put up with it.
I'd go for number 2 personally. Even though pirates might get their hands on your game you're still making money by the legit sales through that portal.
I don't look at piracy as costing me money personally. Unless you're having to eat up bandwidth costs for those pirated downloads then I'm not sure how much money people actually lose through it.
How many folk who pirate the game would otherwise buy it? Very very few I reckon.
Basically if the sales are anyway half decent then I'd stick with the portal. If you think the pirates are costing you money imagine what the portal must be thinking. If they thought they were losing that much cash you can bet there'd be a fix available very very quickly.