Have you tried different positions? A simple pillow under the woman's butt drastically changes the angle and increases the chance at hitting the clit. Doggy style does the same thing really which is why almost every woman on the planet prefers that position. Doggy is also good because either person can reach down and manually stimulate the clit. Also try closing her legs and go in circles instead of the usual.
Maybe this is obvious to everyone else but the clit is actually located between the inserted male penis and the mans hips so maybe instead of thrusting in and out if he'd lift up and down you'd hit the clit from two different directions. I dunno I'd try this immediately if I had a partner atm. Someone else do it for great justice!