As Dabigamc explained perfectly in his solution you need to use the red bouncing MEs to beat the boss with his own ammunition.
I found the last part in which he was running away from you extremely hard. I just could not find a good spot to place my red ME, so that the bullets bounces back and hits the boss.
I found a video which shows a good spot to place your ME. The walkthrough in the video is not the best but at least it shows one consistently working spot to place the ME. I still needed a few tries to get it right, but that was just me messing up the last part of the race. Unfortunately the video is not in English, so sorry for that but it was the only one I found.
He places the ME that kills the robot vacuum at minute 24:35. So feel free to jump directly to this point.
The boss fight itself starts around 15:20. So if you need help on the first 2 parts of the fight you can also jump to this point in the video.
(Video credit: Sazzle)
Hope this helps you guys :-)
Any improvements? Please let me know in the comments below