Destroy all enemies in the first canyon, and some in the path to the 2nd.

Speed boost all the way to the 3rd canyon and destroy the fighters and missile tanks as fast as possible. Reti will teleport to you and skip a chunk of time, but he will be at half health. (or more if he has taken hits.) Destroy the very first tank, and the ones in the more wider gaps in the path to the final canyon. Fly close to Reti at the entrance. (real close, or he dies)

There is however a major problem. after many suffering attempts. I manage to get Reti near to where he lands, but he keeps dying before he can. When doing the skip, it makes him take chunks of damage at certain points. I'm not entirely sure if its based on where he is, or you are, but this happens as soon as Rhys says, "This is where it gets narrow."

How ever, if you do this around 1:50, he will not take damage. Sadly you will have to wait for him to get near the 2nd canyon by that time.