Try to do a deep side lunge. The straight leg will be the one getting the stretch. Try it with an upright torso. You can also place a chair in front of you to hold on to, or place your hands on the ground in front of you, and stick your rear end out. This will help pull the muscles in the inner and back of the thigh right down to the knee. You can also roll a tennis ball or softball up and down along the inside of the thigh.