To echo supernova's advice... though it is definitely easier to handle a shotgun with a stock, it is by no means impossible to effectively shoot a PGO shotgun as long as you practice and use a good technique. This might be hard to convey over Interwebz but I'll try...
Two methods I have found work really great for PGO shotgun are:
1. Instead of firing from the hip or firing with the shotgun out in front of your face (as if it had an imaginary stock), hold the shotgun at chest level and rest your shooting side forearm along your chest parallel to the ground. Within close range, shooting level from your chest assists with your aim since your whole torso helps you reference where the shotgun is pointing. Your arm braced against your chest aids in managing recoil.
2. Use a single point sling and hold the shotgun out in front of you (as if it had an imaginary stock) but push out with both hands making the sling taught. I think this feels weird to some people who are used to pulling in the stock tight with a shotgun and you are now doing the reverse but this greatly mitigates the recoil. I feel this method takes more practice and doesn't allow you to shoot quite as fast as 1 above, but the added benefit is you can still aim down the barrel/bead.
As supernova said, practice lots with light loads and you'll get the hang of it.
I also have no shame in admitting I only shoot birdshot or reduced recoil buck/slug through my PGO shotgun EVER because I r too scared to shoot the heavy stuff heh
