Real easy to do on the first boss area, the cat, as soon as the boss area starts move to the top of the screen straight away and when there keep moving left to right whilst staying at the top to dodge the green balls, the laser eyes and claw can not get you here, simply dodge for 30 secs without shooting, this isn't to difficult as the green balls are quite slow and infrequent, don't shoot and after 30 secs and you'll get your pop, made a YouTube vid for this which will be much easier to follow