Basically what you can do for training by yourself is to retrain the device for your voice. You'll say consecutive times the wake words as they are prompted by the app.
I found a post stating you should tell the wake words all around your home to get different conditions better taken in care. My claim is that the same would apply if you imitate little bit differently your accent in every time.
Disclaimer: This procedure goes through the wake words, so I am not 100% sure if this is enough to catch all nuances.
In other hand Google asks the words so many times it is sufficient, so maybe they know when they get enough data.
Idea about different locations from Google Support