This is an exercise that old time body builders liked to use to increase the size of their chest. In the old days, they didn't have steroids and protein shakes, so they found other ingenious ways to make themselves look bigger.
Many decades ago, a body builder by the name of Peary Rader developed one such exercise, which I think can be very beneficial for people with PE.
It's called the Rader chest pull, and if done correctly, it can produce an immense pull on your sternum, so much so that I've had to ease off on it a bit because the force of the pull was starting to hurt me.
How to do it (see image bellow for better visualization):
1. Find a vertical object, no wider than your head, that you can grip at head hight. A door frame is perfect for this, but you can use other things as well, like a door or a metal bar.
2. Grip the object firmly at head height with your legs at shoulder's length apart. The elbows can be slightly bent for more force.
3. Breathe in deeply into your stomach. Use the diaphragm.
4. Pull with your arms towards your pelvis, activating your back muscles. While doing so, also bend your spine slightly, pushing the chest out and up. For added force you can dip down a bit by bending your knees slightly, and also arch your head back a bit.
During this move you should hold your breath but do not tighten your abdominal muscles. Instead, relax them completely.5. Hold this position for 3+ seconds. How long you can hold it depends on how much you'll train this. Start with 3s, and work your way up as you train this each day.
6. Release your breath and return to the pose described in step 2.

(Blue arrow - position of your spine, head and chest)
(Red arrow - direction in which the pulling force is applied)
Do this for 20 repetitions. How many sets you do is up to you, but try to do 1 set each day.
A few tips before you do this exercise:
It's best to do it while you're still catching your breath after an anaerobic exercise.
Do it while properly warmed up and stretched well to prevent unnecessary pain.
If it starts getting painful for you, use less force. Yes, more force may quicken your PE recovery, but if you pull a ligament you'll be out of commission for months.
The feeling you get while doing this should be mildly uncomfortable. You'll feel like something is sucking your sternum out.
Take it slow and do it smart.