Mirroring or shadowing is definitely helpful with building the mouth muscles. And you can mirror just about anything, but it is best to listen to it, have the script readily available, and then repeat. Focus on intonation and stressing when saying words rather then the number of syllables that are in each word. Exercise your mouth muscles to get used to a different accent. Rinse and repeat. Try to do this for 5-10 mins/day, and if you can do it a few times per day, then your goals will be achieved much quicker.