I’m currently in the market for an Audi, and the C7.5 S7 has caught my eye. I absolutely love the way it looks, but I’m not a fan of the plastic part in the rear seats. I know the same generation A7 has a regular three-seater setup. Has anyone tried replacing it with a cushion or transferring parts from the A7?
You’d probably need a whole new seatback and deal with the seatbelt receptacles. Not really cost-efficient. An A7 might be better if you need the third seat.
Easier to have s*x without the plastic 
How is buying a different car more cost-efficient than just installing seats? He’s looking at around $1k for used seats and about $200 for the receptacle and seatbelt from OEM.
Maybe an S6 lower seat cushion would fit, but you’d still miss the shoulder belt, so it’s not really worth it.
I’d be more worried about getting a third seatbelt in there.
If he replaces the whole bench, he could get the middle seatbelt since it comes from the top of the seat.
I saw someone on Audizine measure and make a padded cover for it.
I feel sorry for anyone who has to sit there. The car is designed for 4, not 5.
I had no idea the A7 had a 5-seater option. Why would they change it?
Check your local laws; in Europe, you’re not allowed to change from a 4 to a 5-seater without reclassification.
No reputable shop will do this as it alters the safety of the car. You might find a sketchy upholstery shop that will take on the job.