Fingers spread out and tips touching the back of your skull(where your neck meets your head), lying down, apply gentle but firm pressure on your scalp(trimmed fingernails) to the point of dragging them firmly from the base of your skull to where your hairline starts. Twisting the positions of your hands to cover places your missed before. Then use your palm to stretch and twist firmly all over. You should start feeling your head warming up, repeat for 5-7 mins for 5 times a day while talking the words you find difficult. Notice how your speech improves in a month or two. Edit: Also as you're lying down saying those words you'll notice you have a greater air flow as your chest is expanded, you're training your airway to let you speak unobstructed. Note: This is anecdotal and might not work for you. Right now my speech is near perfect. Though I stopped the frequency.