It's not all that difficult, I just went back and beat it first try (I'm stuck on lvl 45).
Fire to the upper left and stick to the wall, now fire upwards so that you are on the ceiling about 30-45 degrees to the left of the butterfly. Fire down and bounce into the upper right section, freeing the butterfly in the upper left in the same shot. Now you have several shots remaining to take out the last two butterflies, and you're done