So pretty much it does one of a few things. Or something quite similar.
- IFrame to a page with a javascript redirect
- Javascript creating an image object that happens to really be the cookie drop location. Then immediately removing it after it fires.
Either of which are detectable, but harder.
People, the issue with getting nailed with cookies stuffing(especially on EPN now) is the delay between the cookie drop and the purchase(or lack of a purchase). Nothing can really fix that.