Custom code to replace product lightbox result

Evening,

Im desperately trying to find a way to lightbox my products – but instead of it lightboxing the single product page I actually need to pop some code into each individual product’s CSS to make it lightbox to a specific document/url on my domain instead.

I am sure this HAS to be possible but Im just getting caught in circles trying to figure out how I can manipulate things to get it to work.

Any help would be greatfully recieved!