I just found this out last night, in case anyone else finds themself in this situation.I was in a GDI MRL just outside the Nod base entrance. We were getting shot at my snipers and raveshaws up on top of the wall. I was almost under the wall with my MRL when I did this. I faced away from the wall and aimed up a the snipers and fired the missles. The missles shot forward and way up into the air and then back down on top of the wall... killing all of the snipers. I would think this would work even if you were farther away from the wall as well.
It was much easier than trying to shoot directly at them.. even tanks and infantry can sometimes have trouble hitting them from the ground.
Nothing fancy.. but it worked for me last night so I thought I'd share.