I know it can be done, but I've been awak for 36+ hours so I'm in no state to try and think of it.
But wouldn't it be better anyhow to place the cpalead gateway on the browse page versus on the index? This way when they arrive to your site, they aren't immediately hit with the gateway, most people would just hit the back button at this point. Wouldn't you if the very first thing you saw on a site was an advert survey?
Instead, you can explain on the index about the cpalead survey, and why you're using it and how it benefits them (ie, no other ads on proxified pages, etc). Now, they'll be knowingly going forward to the proxified page and expecting to fill out a survey. And if they don't want to fill one out, hey at least they're on the index and may be more inclined to exit via say an adsense ad or to your other proxy sites, lists, etc.
Just my thoughts on it, Cheers!