Decocking is still the best option, if the barrel and cocking lever can travel back far enough without hitting your straps. I see the mess you have with the failing compressor. There's better ways to contain the receiver and barrel assembly but you can deal with that AFTER you get out of this predicament.
I sent you a PM with suggestions. If you can, try to shoot a photo of the front of the trigger group where the sear contacts the piston. And CAREFULLY see if you can break the barrel and how far in the cocking cycle it will go before hitting your straps. If it can be pulled back far enough to put pressure on the piston and spring, you can use a jewlers screwdriver or similar tool to lift the sear to release the piston and spring. THIS WILL PUT THE FULL load of the spring on the barrel you are holding, so BE PREPARED!!!!! If you do not control the barrel and have the entire setup locked down securely, it will most definately slam down and bend the barrel. Or worse, cause you bodily injury. BE CAREFUL!!!!!
If the barrel will not cycle to be able to decock, then you will have to dry fire the gun. This can cause damage like a broken spring or other internals. To help lessen the chances of this, get yourself a thick cloth. Put it over the end of the barrel (WITHOUT YOUR HAND OVER THE END OF THE BARREL) to help put some resistance there to prevent the piston from slamming too hard. Then release the sear to fire it. Hope some of this helps but most importantly, BE CAREFUL. Guns and parts can be replaces, body parts can not.