Happened to me this spring in a huge baetis hatch. After about 20 casts, I finally timed it right and caught the one fish I wanted, 21" rainbow. The only reason I got him (no hatch matcher), was because I put a big fat juicy stimulator within a half inch of his head.
Actually, twice. A big brown was rising near the shore on a stocked lake, and I put a #18 adams right beside his next obvious meal (a big drowned dragonfly). I hooked him, then lost him. Fairplay? Probably not.
I think the best option is just to put it as close to their feeding lane as possible.