For starters, foxyproxy does NOT mask the IP address of you, the viewer (that is straight from their website). So, technically, the same ip address will be showing as visiting the site. I think Alexa takes that into consideration.
Next, you better ensure you have no Adsense on there, because if Gxxgle sees the same OS, monitor settings, same browser, and the same IP address hitting that site every 30 secs, kiss your account goodbye.
These gimmicks all work to get your site to around 500,000 (maybe even to 250,000) but that is it.