Find out what it is worth for the client.
If they are willing to pay for you to hang out around the sofa for a few days than do what the the Sweendog suggests.
Most clients will not.
Next step, you tell the client: "Here is how you can save money."
Their eyes light up.
Have them (
with all the necessary disclaimers after all you did not do that on their sofa, it is their problem) (who knows, it might also be a good time to discuss corporal punishment
)
Anyhow, back to our subject- Have the client take the foam (filling) material out put in a plastic bag and soak for two days with a good natural enzyme product and let it sit.
Then they should remove it and let it dry.
When you come to clean the sofa (cushion should be completely dry), you will still need to treat the urine on the microfiber and re-install the cushion. Use the trick of putting the cushion in a plastic bag, vacuuming so it shrinks and putting it back.
Voila!
You are their hero.
At least till the cat/spouse/drunk buddy does it again.