If you tell me how a "popup" or "popunder" is different from a normal page request when done with LWP, then I can tell you how a webserver might differentiate between them.

Before you start faking hits to a website, I can only recommend you to understand the HTTP protocol and the other side, how hits, visits and page impressions are actually counted. Having some understanding of sniffing tools and/or protocol analyzing tools is also of advantage, but this site has its focus on Perl, and none of this is central to Perl.