This, for example, from T-something:
Press your neck forcefully against an immovable force (your hand) on each side, and front and back, holding your head at the temples/forehead. Isometrically hold for 30 seconds, really hard. Repeat 3x week (it'll take minutes, you know) and you could maybe even increase the volume, and obviously as you get stronger it'll increase in intensity. Good luck.