This is a Hatha Yoga technique for stretching out the inner groin. I am not a professional, but I have practiced for about 2 years. Here are 2 stretches.
First (easiest): Supine Bound Angle Pose
Sit on the ground and bend your knees so that your feet are flat on the ground. Maintain good posture (back erect, head in line with spine, do not be rigid). Slowly drop your knees outward and bring the soles of your feet together (like your praying with them). Arch your back and place your hands behind you. Slowly lower to your elbows and then lower yourself carefully to the floor. You should be laying on the middle of your back, head resting on the floor, buttocks resting on the floor. Ensure that your tailbone is not digging into the ground. Allow your lower back to arch a little, naturally, comfortably. Your knees should be apart and off the floor (at first) and your outer ankles should be resting comfortably with the soles of your feet together. Just lay there and allow the weight of your legs to drop your knees further and further to the floor. Do not force them. Over time you will notice more limber-ness in your groin.
Second (more difficult): Triangle Pose
Stand upright and place your feet a little wider than shoulder width apart. Keep your legs straight, but do not lock your knees. Bend over and touch the floor. When you can place your hands flat on the floor in this posision you can then safely move to Triangle Pose by rotating from your hips to your right and then left ankle.
It is easiest to place your hand on your calf or ankle (depending on flexibility) to maintain balance. Your torso should be straight and parallel with the ground (eventually you will be able to put your hand flat on the floor behind and right next to your foot). Your chest should be pointed forward. Raise your other arm to the sky, perpendicular to the floor. Hold this pose for as long as you can on each side (no more than 5-10 minutes is needed).
Go slowly with these poses as you are not practicing a group of asanas (Yoga Poses) together, and you can seriously injur yourself if you take it to fast or try to push yourself too far. Warm up before every stretch with some normal warm up stretching.
Look up Supine Bound Angle Pose and Triangle Pose for some pictures to guide you to the correct posture, thus avoiding some injury.
You should see results in about a month, tops, if you practice every other day. Take it slow and you'll be straddling 23" in no time.