Like this guy, but he doesn't even know I exist!?

Okay, so here's the thing.. I go to a girls private school where every week we visit an all boys private school and our grade (11) listen to a talk together, given by some lecturer about a specific topic. Our row is at the back, and all the guys sit infront. I know this sounds kinda sad but I have literally fallen for this guy there, and he sits in the row infront of us. I just dont know how to catch his attention or ANYTHING. I really need some advice, how would I get his attention, or catch his eye because theres not really any chance for us to talk as we have to rush out as soon as its over, and we only really see the back of their heads whilst listening to the talk, to be honest. WHAT CAN I DOOOOO? Nothing silly please, thanks.