Hi Thomas,
Not sure if I can help but maybe this will work:
Make an object (object A) that is as big (or a little bit bigger) as the view of the camera, also in depth. Animatie so it moves with the camera. Use object A to dynamic paint the hair particle on the object it’s on. And put object A on a different layer so it will not render.
This way, I think, the particle will only show up in the part of where object A hits the emitter.
HAven’t tested it but i think it should work 