First I suggest you accept it and just superread faster. If you're subvocalising you're not superreading, speed it up.
Next thing you can do is play some nature sounds in the background not music but sounds like rain, ocean, wind blowing in the trees etc, these help to reduce subvocalisation.
Another thing you can try is saying the letter A over and over while you read, You need to do this for at least 30 minutes but you'll find subvocalisation will be reduced if you stick with it. Just the one letter, no alphabet no song, just A over and over.
Alex
