[V ger]

This usually works well.
Drill a hole or holes in the plywood base or back of the cushion.
Cut notches or drill holes in a short section of reinforced PVC hose.
Tape the hose to the cushions plywood backing.
Place a some bubble wrap bubble side against the hose and plywood to keep the bag from sealing the hose.
Place the cushion in a plastic bag.
Seal the bag with tape where the PVC hose exits the bag.
Connect the hose to a vacuum pump. Not a vacuum cleaner.
Drawing the air out of the sealed bag will compress the cushion squeezing much of the water out. The low pressure will speed evaporation. A little gentle heat will speed the drying process. You may have to repeat this a few times to get complete drying.